Surgical spinal correction

ABSTRACT

A method is provided for planning, performing, and assessing of surgical correction to the spine during a spinal surgical procedure. This method is implemented by a control unit through a GUI to digitize screw locations, digitize anatomical reference points, accept one or more correction inputs, and generate one or more rod solution outputs shaped to engage the screws at locations distinct from the originally digitized locations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/027,904 (currently pending) filed on Apr. 7, 2016, which is anational stage entry of PCT Patent Application Serial No. PCT/US14/59974filed on Oct. 9, 2014, which claims the benefit of priority fromcommonly owned U.S. Provisional Patent Application Ser. No. 61/888,990,entitled “Systems and Methods for Performing Spine Surgery,” and filedon Oct. 9, 2013, the entire contents of which is hereby expresslyincorporated by reference into this disclosure as if set forth in itsentirety herein.

FIELD

The present application pertains to spine surgery. More particularly,the present application pertains to systems and methods related to theplanning, performing, and assessing of surgical correction to the spineduring a spinal surgical procedure.

BACKGROUND

The spinal column is a highly complex system of bones and connectivetissues that provide support for the body and protect the delicatespinal cord and nerves. The spinal column includes a series of vertebralbodies stacked atop one another, each vertebral body including an inneror central portion of relatively weak cancellous bone and an outerportion of relatively strong cortical bone. Situated between eachvertebral body is an intervertebral disc that cushions and dampenscompressive forces exerted upon the spinal column. A vertebral canalcontaining the spinal cord is located behind the vertebral bodies. Thespine has a natural curvature (i.e., lordosis in the lumbar and cervicalregions and kyphosis in the thoracic region) such that the endplates ofthe upper and lower vertebrae are inclined towards one another.

There are many types of spinal column disorders including scoliosis(abnormal lateral curvature of the spine), excess kyphosis (abnormalforward curvature of the spine), excess lordosis (abnormal backwardcurvature of the spine), spondylolisthesis (forward displacement of onevertebra over another), and other disorders caused by abnormalities,disease, or trauma (such as ruptured or slipped discs, degenerative discdisease, fractured vertebrae, and the like). Patients that suffer fromsuch conditions often experience extreme and debilitating pain, as wellas diminished nerve function. Posterior fixation for spinal fusions,decompression, deformity, and other reconstructions are performed totreat these patients. The aim of posterior fixation in lumbar, thoracic,and cervical procedures is to stabilize the spinal segments, correctmulti-axis alignment, and aid in optimizing the long-term health of thespinal cord and nerves.

Spinal deformity is the result of structural change to the normalalignment of the spine and is usually due to at least one unstablemotion segment. The definition and scope of spinal deformity, as well astreatment options, continues to evolve. Surgical objectives for spinaldeformity correction include curvature correction, prevention of furtherdeformity, improvement or preservation of neurological function, and therestoration of sagittal and coronal balance. Sagittal plane alignmentand parameters in cases of adult spinal deformity (ASD) are becomingincreasingly recognized as correlative to health related quality of lifescore (HRQOL). In the literature, there are significant correlationsbetween HRQOL scores and radiographic parameters such as SagittalVertical Axis (SVA), Pelvic Tilt (PT) and mismatch between pelvicincidence and lumbar lordosis.

The SRS-Schwab classification of ASD was developed to assist surgeonswith a way to categorize ASD, and provide methods of radiographicanalysis. This classification system helps provide a protocol forpre-operative treatment planning and post-op assessment. The currentenvironment to utilize this classification system requires surgeons toexamine pre-operative patient films and measure pelvic incidence, lumbarlordosis, pelvic tilt, and sagittal vertical axis either manually orthrough the use of pre-operative software. After the procedure, thesurgeon examines the post-operative films and measures the sameparameters and how they changed as a result of the surgery. A needexists for systems and methods for assessing these and other spinalparameters intraoperatively and assessing changes to theseintraoperative spinal parameters as a surgical procedure progressestowards a pre-operative plan.

During spinal surgeries, screws, hooks, and rods are devices used tostabilize the spine. Such procedures often require the instrumentationof many bony elements. The devices, for example rods, can be extremelychallenging to design and implant into the patient. Spinal rods areusually formed of stainless steel, titanium, cobalt chrome, or othersimilarly hard metal, and as such are difficult to bend without somesort of leverage-based bender. Moreover, a spinal rod needs to beoriented in six degrees of freedom to compensate for the anatomicalstructure of a patient's spine as well as the attachment points (screws,hooks, etc.) for securing the rod to the vertebrae. Additionally, thephysiological problem being treated as well as the physician'spreferences will determine the exact configuration necessary.Accordingly, the size, length, and particular bends of the spinal roddepends on the size, number, and position of each vertebra to beconstrained, the spatial relationship amongst vertebrae, as well as thescrews and hooks used to hold the rods attached to the vertebrae.

The bending of a spinal rod can be accomplished by a number of methods.The most widely used method is a three-point bender called a FrenchBender. The French bender is a pliers-like device that is manuallyoperated to place one or more bends in a rod. The French bender requiresboth handles to operate and provides leverage based on the length of thehandle. The use of the French bender requires a high degree of physicianskill because the determination of the location, angle, and rotation ofbends is often subjective and can be difficult to correlate to apatient's anatomy. Other methods of bending a rod to fit a screw and/orhook construct include the use of an in-situ rod bender and a keyholebender. However, all of these methods can be subjective, iterative, andare often referred to as an “art.” As such, rod bending and reductionactivities can be a time consuming and potentially frustrating step inthe finalization of a complex and/or long spinal construct. Increasedtime in the operating room to achieve optimum bending can be costly tothe patient and increase the chance of the morbidity. When rod bendingis performed poorly, the rod can preload the construct and increase thechance of failure of the fixation system. The bending and re-bendinginvolved can also promote metal fatigue and the creation of stressrisers in the rod.

Efforts directed to computer-aided design or shaping of spinal rods havebeen largely unsuccessful due to the lack of bending devices as well aslack of understanding of all of the issues involved in bending surgicaldevices. Recently, in U.S. Pat. No. 7,957,831 to Isaacs, there isdescribed a rod bending system which includes a spatial measurementsub-system with a digitizer to obtain the three dimensional location ofsurgical implants (screws, hooks, etc.), software to convert the implantlocations to a series of bend instructions, and a mechanical rod benderused to execute the bend instructions such that the rod will be bentprecisely to custom fit within each of the screws. This is advantageousbecause it provides quantifiable rod bending steps that are customizedto each patient's anatomy enabling surgeons to create custom-fit rods onthe first pass, thereby increasing the speed and efficiency of rodbending, particularly in complex cases. This, in turn, reduces themorbidity and cost associated with such procedures. However, a needstill exists for improved rod bending systems that allow for curvatureand deformity correction in fixation procedures, provide the user withmore rod bending options, and accommodate more of the user's clinicalpreferences.

SUMMARY

The present invention includes a system and methods for rod bending thatenable a user (e.g., surgeon) to customize rod bend instructions to suitthe desired correction of a patient's spinal condition.

According to a broad aspect, the present invention includes a spatialtracking system for obtaining the three-dimensional position informationof surgical implants, a processing system with software to convert theimplant locations to a series of bend instructions based on a desiredcorrection, and a mechanical rod bender for bending a surgical linkingdevice to achieve the desired spinal correction.

According to another aspect of the present invention, the spatialtracking system includes an infrared (IR) position sensor and at leastone IR-reflective tracking array attached to at digitizer pointer usedto digitize the surgical implant location. The spatial tracking systemis communicatively linked to the processing system such that theprocessing system may utilize the spatial position information togenerate bend instructions.

According to another aspect of the present invention, the processingsystem is programmed to generate bend instructions based on one or moresurgeon-prescribed clinical objectives. For example, the processingsystem may be programmed to create a custom bend, adjust one or morepoints to which the rod will be bent to, suggest a pre-bent rod option,provide spinal correction in the sagittal plane, provide spinalcorrection in the coronal plane, and provide correction to achieveglobal spinal balance, and as well as perform a plurality ofpredetermined functions. The processing system may be further programmedto receive preoperative spinal parameters, input planned or targetspinal parameters, and/or track intraoperative measurement of thoseparameters. The processing system is further configured to preview anddisplay the results of these clinical objectives and/or predeterminedfunctions to the user in a meaningful way.

According to another aspect of the invention, one or more surgicalprocedures may be performed using various embodiments of the system.

According to another aspect of the invention, there is provided a systemfor intraoperative planning and assessment of spinal deformitycorrection during a surgical spinal procedure, the system comprising: aspatial tracking system comprising an IR sensor and an IR trackingarray, said IR tracking array being arranged along a proximal end of asurgical pointer tool capable of digitizing the location of an implantedsurgical device and relaying to the spatial tracking system via the IRsensor; a control unit in communication with the spatial trackingsystem, said control unit being configured to: (a) receive the digitizedlocation data of a plurality of implanted screws; (b) receive thedigitized location data of at least one anatomical reference point; (c)generate at least one virtual anatomic reference line based on thedigitized location data of said at least one anatomical reference point;(d) accept one or more spine correction inputs; and (e) generating atleast one rod solution output shaped to engage the screws at locationsdistinct from the digitized location.

According to one or more embodiments, the spine correction input is aspine correction in the coronal plane. According to someimplementations, the spine correction input comprises aligning all ofthe digitized screw locations relative to the CSVL in the coronal plane.According to some implementations, the system generates a rod solutionoutput that includes T a vertically straight rod along at least aportion of the length.

According to some implementations, the virtual anatomic reference lineis the central sacral vertical line (CSVL). According to someimplementations, the at least one anatomical reference point comprisesat least two points that correlate to the CSVL. According to otherimplementations, the at least one anatomical reference point comprisestwo points that lie along the CSVL. According to some implementations,the at least two points are the left iliac crest, the right iliac crest,and the midpoint of the sacrum. According to some implementations, theat least one anatomical reference point comprises a superior point andan inferior point on the sacrum.

According to one or more embodiments, the control unit is configured togenerate at least one measurement value based on at least twoanatomically-based reference lines. According to some implementations,this measurement value may be an offset distance between the tworeference lines. According to some implementations, the two referencelines are the central sacral vertical line (CSVL) and the C7 plumb line(C7PL). According to yet other implementations, the control unit isfurther configured to assess intraoperative spinal balance based on arelationship between said CSVL and C7PL and communicate that assessmentto a user. In some implementations, the r relationship may be based onthe coronal offset distance between the CSVL and C7PL. In yet otherimplementations, the communication may be a color. For example, thecommunication may be such that a first color designates an offsetdistance indicating a balanced spine within the coronal plane and asecond color designates an offset distance indicating an unbalancedspine within the coronal plane.

According to one or more embodiments, the control unit is configured togenerate at least one measurement value based on at least oneanatomically-based reference point. According to one or moreimplementations, the measurement value comprises an intraoperativelumbar lordosis angle and a planned pelvic incidence angle. According tosome implementations, the control unit is further configured to assessintraoperative spinal balance based on a relationship between anintraoperative lumbar lordosis angle measurement and a planned pelvicincidence angle. In some instances, the lumbar lordosis angle and pelvicincidence angle may be measured at least once during the operationprogress. According to some implementations, the relationship betweenlumbar lordosis and pelvic incidence may be based on the variancebetween the intraoperative lumbar lordosis angle and the planned pelvicincidence angle. According to some implementations, the communicationmay be a color. For example, a first color may designate varianceindicating a balanced spine within the sagittal plane and a second colordesignates a variance distance indicating an unbalanced spine within thesagittal plane.

BRIEF DESCRIPTION OF THE DRAWINGS

Many advantages of the present invention will be apparent to thoseskilled in the art with a reading of this specification in conjunctionwith the attached drawings, wherein like reference numerals are appliedto like elements and wherein:

FIG. 1 is a surgical procedure setup depicting the components of asurgical planning, assessment, and correction system, according to oneembodiment;

FIG. 2 is a perspective view of one embodiment of a digitizer array inthe closed position comprising part of the system of FIG. 1;

FIG. 3 is an exploded perspective view of the digitizer array of FIG. 2;

FIG. 4 is a perspective view of the digitizer array of FIG. 2 in theopen position;

FIG. 5 is a front view of one embodiment of a digitizer pointer assemblycomprising part of the system of FIG. 1;

FIG. 6 is a perspective view of various surgical pointers compatiblewith the digitizer array of FIG. 2;

FIG. 7 is a partial perspective view of the offset pointer of FIG. 6 ina collapsed position;

FIG. 8 is a partial exploded view of the offset pointer of FIG. 6;

FIG. 9 is a partial perspective view of the offset pointer of FIG. 6 inan extended position;

FIG. 10 is a flowchart depicting the steps of the spatial trackingalgorithm according to one embodiment;

FIG. 11 is a flowchart depicting the rod bending workflow according toone embodiment;

FIG. 12 is a flowchart depicting the steps in generating a rod solutionaccording to a first embodiment;

FIG. 13 is a flowchart depicting the steps in generating rod solutionaccording to a second embodiment;

FIG. 14 is a flowchart depicting the steps in generating a rod solutionaccording to a third embodiment;

FIG. 15 is a flowchart depicting the steps of the rod bending processaccording to a first embodiment;

FIG. 16 is a screen shot depicting an example setup screen of the systemof FIG. 1;

FIG. 17 is a screen shot depicting an example IR positioning sensorsetup screen of the system of FIG. 1;

FIG. 18 is a screen shot depicting an example screw locationdigitization screen during a first step in the Acquire Screws step ofFIG. 15;

FIG. 19 is a screen shot depicting an example screw locationdigitization screen during a second step in the Acquire Screws step ofFIG. 15;

FIG. 20 is a screen shot depicting an example screw digitization screenduring a third step in the Acquire Screws step of FIG. 15;

FIG. 21 is a screen shot depicting an example bend instructions screenin the Bend Instructions step of FIG. 15;

FIG. 22 is a flowchart depicting the steps of the rod bending processaccording to a second embodiment;

FIG. 23 is a screen shot depicting an example Advanced Options menuscreen of the system of FIG. 1;

FIG. 24 is a screen shot illustrating a first example screen of anAdjust Points feature according to one embodiment;

FIG. 25 is a screen shot illustrating a second example screen of theAdjust Points feature of FIG. 24;

FIG. 26 is a screen shot illustrating a third example screen of theAdjust Points feature of FIG. 24;

FIG. 27 is a screen shot illustrating a first example screen of aPre-Bent Preview feature according to one embodiment;

FIG. 28 is a screen shot illustrating a second example screen of thePre-Bent Preview feature of FIG. 27;

FIG. 29 is a screen shot illustrating a third example screen of thePre-Bent Preview feature of FIG. 27;

FIG. 30 is a screen shot illustrating a first example screen of aSagittal Correction feature according to one embodiment;

FIG. 31 is a screen shot illustrating a second example screen of theSagittal Correction feature according to the first embodiment;

FIG. 32 is a screen shot illustrating a first example screen of theSagittal Correction feature according to a second embodiment;

FIG. 33 is a screen shot illustrating an additional example screen ofthe Sagittal Correction feature according to the first and/or secondembodiment;

FIG. 34 is a screen shot illustrating a first example screen of theCoronal Correction feature according to a first embodiment;

FIG. 35 is a screen shot illustrating a second example screen of theCoronal Correction feature according to the first embodiment;

FIG. 36 is a screen shot illustrating a first example screen of theCoronal Correction feature according to a second embodiment;

FIG. 37 is a screen shot illustrating a second example screen of theCoronal Correction feature according to the second embodiment;

FIG. 38 is a screen shot illustrating a first example screen of theCoronal Correction feature according to a third embodiment;

FIG. 39 is a screen shot illustrating a second example screen of theCoronal Correction feature according to the third embodiment;

FIG. 40 is a screen shot illustrating a third example screen of theCoronal Correction feature according to the third embodiment;

FIG. 41 is a screen shot illustrating a fourth example screen of theCoronal Correction feature according to the third embodiment;

FIG. 42 is a screen shot illustrating a first example screen of theCoronal Correction feature according to a second embodiment;

FIG. 43 is a screen shot illustrating a second example screen of theCoronal Correction feature according to the second embodiment;

FIG. 44 is a screen shot illustrating a third example screen of theCoronal Correction feature according to the second embodiment;

FIG. 45 is a screen shot illustrating a first example screen of theCoronal Correction feature according to the third embodiment;

FIG. 46 is a screen shot illustrating a second example screen of theCoronal Correction feature according to the third embodiment;

FIG. 47 is a screen shot illustrating a third example screen of theCoronal Correction feature according to the third embodiment;

FIG. 48 is a screen shot illustrating a fourth example screen of theCoronal Correction feature according to the third embodiment;

FIG. 49 is a screen shot illustrating a fifth example screen of theCoronal Correction feature according to the third embodiment;

FIG. 50 is a flowchart illustrating the steps of the Global SpinalBalance feature according to one embodiment;

FIG. 51 is a flowchart illustrating the steps of the Global SpinalBalance feature according to a second embodiment;

FIG. 52 is a screen shot illustrating a first example screen of theGlobal Spinal Balance feature in pre-operative mode;

FIG. 53 is a screen shot illustrating a first example screen of theGlobal Spinal Balance feature in target mode;

FIG. 54 is a screen shot illustrating a second example screen of theGlobal Spinal Balance feature in target mode;

FIG. 55 is a screen shot illustrating a first example screen of theGlobal Spinal Balance feature in intraoperative mode;

FIG. 56 is a screen shot illustrating a second example screen of theGlobal Spinal Balance feature in intraoperative mode;

FIG. 57 is a screen shot illustrating a third example screen of theGlobal Spinal Balance feature in intraoperative mode;

FIG. 58 is a screen shot illustrating a fourth example screen of theGlobal Spinal Balance feature in intraoperative mode;

FIG. 59 is a screen shot illustrating a fifth example screen of theGlobal Spinal Balance feature in intraoperative mode;

FIG. 60 is a screen shot illustrating a first example screen of aCoronal Assessment and Correction feature according to a firstembodiment;

FIG. 61 is a screen shot illustrating a second example screen of aCoronal Assessment and Correction feature according to the embodiment ofFIG. 60;

FIG. 62 is a screen shot illustrating a third example screen of aCoronal Assessment and Correction feature according the embodiment ofFIG. 60;

FIG. 63 is a screen shot illustrating a fourth example screen of aCoronal Assessment and Correction feature according to the embodiment ofFIG. 60;

FIG. 64 is a perspective view of one embodiment of a mechanical rodbender comprising part of the system of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin development of any such actual embodiment, numerousimplantation-specific decisions must be made to achieve the developers'specific goals such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure. The systems and methods disclosed herein boast avariety of inventive features and components that warrant patentprotection, both individually and in combination.

With reference now to FIG. 1, there is shown, by way of example, oneembodiment of a surgical planning, assessment, and correction system 10including a spatial tracking system 12 to obtain the location of one ormore surgical implants 14, a control unit 16 containing software toconvert the implant locations to a series of bend instructions, and abending device 18 to execute the bend instructions.

Preferably, the spatial tracking system 12 includes an IR positionsensor 20, a digitizer pointer 23, as well as other components includingHost USB converter 21. The spatial tracking system 12 is incommunication with control unit 16. The control unit 16 has spatialrelation software and C-arm video import capabilities and iscommunicatively linked to the display 32 so that information relevant tothe surgical procedure may be conveyed to the user in a meaningfulmanner. By way of example, the relevant information includes, but is notlimited to, spatial positioning data (e.g., translational data in the x,y, and z axes and orientation/rotational data R_(x), R_(y), and R_(z))acquired by the IR position sensor 20 and intraoperative fluoroscopicimages generated by the C-arm fluoroscope.

According to one or more embodiments, the system 10 comprises aneuromonitoring system communicatively linked to the spatial trackingsystem 12 and/or the C-arm via the control unit 16. By way of exampleonly, the neuromonitoring system may be the neuromonitoring system shownand described in U.S. Pat. No. 8,255,045, entitled “NeurophysiologicMonitoring System” and filed on Apr. 3, 2008, the entire contents ofwhich are hereby incorporated by reference as if set forth fully herein.

FIGS. 2-9 depict the various components of one or more digitizerpointers 23 for use with the present invention. FIGS. 2-4 detail anexample IR-reflective tracking array 22 component of the digitizerpointer 23. Array 22 includes a housing 34, bilateral shutters 36, and aplurality of IR-reflective spheres 38 arranged in a calculated manner atvarious locations on the array 22 such that their position informationis selectively detectable by the IR position sensor 20. Housing 34comprises a top housing 40, bottom housing 42, and a distal threadedaperture 56 configured to threadably receive the threaded end 78 of astylus (e.g., stylus 24, 26, 28, and/or 30). Top housing portion 40 isfurther comprised of upper portion 44, underside 46, and sides 48. Aplurality of sphere apertures 52 extend between upper portion 44 andunderside 46 and are sized and dimensioned to receive reflective spheres38 within recessed pockets 54. Each side 48 includes cutout 50 sized anddimensioned to receive tongue 70. Bottom housing 42 is comprised of afirst face 58 and a second face 60. The first face 58 includes nestingplatforms 62 and bullet posts 64. Each shutter 36 includes handleportion 66, cover portion 68, tongue 70, interdigitating gear teeth 72,and channel 74 for receiving bullet posts 64. A spring 76 extendsbetween the two shutters 36 and is held in place via spring posts 71.

In an assembled state, each IR-reflective sphere 38 is nested on aplatform 62. Top housing 40 is placed over bottom housing 42 in a snapfit configuration such that each IR-reflective sphere 38 fits within arecessed pocket 54 within its respective sphere aperture 52. Accordingto one implementation, bilateral shutters 36 are positioned over thehousing 34 with tongues 70 sliding into cutouts 50 such that eachshutter cover 68 obscures exactly one half of the IR-reflective sphere38 (for example, the middle IR-reflective sphere 38) as depicted in FIG.2.

As depicted in FIG. 5, the IR-reflective tracking array 22 mates withone or more surgical objects (for example styluses 24, 26, 28, 30). Eachstylus 24, 26, 28, 30 includes a threaded proximal end 78 for matingwith the threaded distal aperture 56 of the IR-reflective tracking array22, elongate shaft 80, and shaped distal tip 82. Shaped distal tip 82may be any shape that is complimentary to, and fits securely within, theshape of a particular screw head. For example, FIG. 6 shows styluses 24,26, 28, and 30 each with a different shaped distal tip designed to matewith different open screw systems, minimally-invasive screw systems, andclosed tulip, iliac, and offset connector systems. The distal tip 82 ispreferably inserted into each screw while orienting the digitizerpointer coaxial to that screw (or other fixation device).

According to some implementations (for example, the implementationsshown with respect to styluses 24, 26, and 28), the length of theelongate shaft 80 is fixed relative to the array 22 such that alldigitized points are a consistent length from the geometry of theIR-reflective markers 38 and position information may be obtained fromthis relationship. According to other implementations (for example, theimplementation shown with respect to offset pointer 30), the length ofthe elongate shaft 80 is adjustable relative to the array 22 such asthat shown with stylus 30, effectively elongating the distance from thedigitized point and the IR-reflective markers. This longer distancetranslates to digitization of a point above the actual screw head basedon the distance the user adjusted the elongate shaft 80. As will beappreciated in conjunction with the discussion below, the resulting bendinstructions would shape a rod that traverses that point above the screwallowing the user to reduce the screw to the rod.

As shown in FIGS. 6-8, offset pointer 30 includes an elongate tubularmember 84 and an inner piston 86. Elongate tubular member 84 iscomprised of a milled helical slot 104 and a plurality of offset depthslots 106 located around the helix that correspond to a plurality ofoffset distances as will be described below. Inner piston 86 includesshaft 88, T-shaped cap 92, springs 94, and bushing 96. The T-shaped cap92 is positioned over the proximal end of the shaft 88 and is preferablywelded to the proximal end 105 of the elongate tubular member 84.Springs 94 are slideably positioned along the length of the shaft 88between the distal end 93 of the T-shaped cap 92 and bushing 96. Bushing96 is positioned over the distal end of the shaft 88. Pin 100 is travelsthrough, and protrudes laterally from, slots 90, 98 on the inner shaft88 and bushing 96, thereby securing the bushing 96 to the inner shaft88. The pin 100 is sized and dimensioned such that it travels throughthe helical slot 104 and be positioned within each of the offset depthslots 106.

The offset pointer 30 gives the user the ability to execute plannedscrew movement by a specific, pre-determined amount. The user insertsthe offset pointer 30 into the screw head. Keeping the distal tip 82engaged to the screw head, the user then selects an offset amount to beadded to the screw and angles the offset pointer 30 in the direction heor she wishes to apply the offset to. To adjust between offset depthslots 106, the shaft 88 is pulled away from the array 22 and twisteduntil the pin 100 falls into the desired offset slot 106. As the shaft88 is pulled, it telescopes in and out of the elongate tubular member 84such that the distance between the shaped distal end 82 and the array 22is increased. For purposes of illustration, FIG. 8 shows the offsetpointer 30 with the pin 100 in the 16 mm offset slot 106 correspondingto a 16 mm offset between the pointer 30 length and the IR-reflectivearray 22. Offset options for sagittal correction may be provided, by wayof example only from 0 mm to 16 mm offsets in 2 mm increments. Thesystem 10 will then acquire position information at that point in spaceas opposed to where the screw sits, allowing for sagittal correction ofone or more vertebral levels.

The digitizer pointer 23 may be used to acquire positional informationabout some or all screw locations. According to a preferred embodiment,the shaped distal tip 82 is coaxially aligned into the screw head andthe array 22 is triggered to register the screw point. Screw locationsmay be digitized in a superior-inferior or inferior-superior direction.According to some implementations, the first screw location digitizedcorrelates to the rod insertion direction component of the bendinstructions (described below). Squeezing handles 66 activates thespring mechanism and permits the shutters 36 to open equally via theinterdigitating gear teeth 72 (FIG. 4). Opening the shutter covers 68exposes the middle IR-reflective sphere 38 and allows the IR trackingarray 22 to be “seen” by the IR position sensor 20 and the position ofthe digitizer pointer 23 to be digitized. In this way, the IR positionsensor 20 only recognizes the digitizer pointer 23 once the middlesphere 38 is exposed which allows for point-by-point tracking andobviates the sensing and digitization of one or more unnecessary datapoints which may occur with prior art systems that continually tracksurgical objects. Further, use of the gear mechanism allows the passiveIR-reflective sphere 38 to be “seen” symmetrically by the IR positionsensor 20, thereby enabling a more accurate calculation of positioninformation by the system 10. According to some implementations, thecontrol unit 16 emits an audible sound to notify the user that themiddle sphere 38 is recognized by the IR position sensor 20 and thescrew point is acquired. Once a point has been registered, the shutterhandles 66 may be released, thereby closing the bilateral shutters 36.This process is then repeated for all screw locations to be digitized.

In accordance with the present invention, there are provided a pluralityof algorithms for achieving rod bends. The surgical bending algorithmsmay be divided into two smaller sub-systems: (1) the spatial locationalgorithms that acquire, collect, and digitize points in space and (2)the bending algorithms that analyze the points and calculate the bendinstructions and rod length needed to bend a rod with the mechanicalbending device 18.

As set forth above, the spatial tracking system 12 measures the sixdegrees of freedom (6 DOF) information for the tracked IR-reflectivespheres 38. These data provide the full pose (position and orientation)of each screw of interest which may then be made available to thealgorithm library to calculate the bend instructions. FIG. 10 is a flowchart indicating the steps of the spatial location data acquisitionprocess according to one embodiment. The system 10 initializes thesensor objects from configuration to connect to, control, and read datafrom the IR position sensor 20 (step 140). The system 10 then inspectsall devices connected to it and finds the device with a device ID thatcorresponds to the IR position sensor 20 (step 141). At step 142, if anIR position sensor 20 is found at step 141, the system 10 continues toestablish a connection with the IR position sensor 20 (step 143).However, if not the system 10 continues to search. After the system 10connects to the IR sensor 20, it then loads a tool file that defines thearray 22 (step 144). After initialization and tool file loading, the IRsensor 20 must prepare for taking data. At step 145, the IR sensor 20 isenabled and ready to generate positional data but is left idle untiltracking is enabled. By way of example and as described with referenceto FIG. 17, selecting the position of the IR sensor 20 with respect tothe patient's body causes the control unit 16 to send the IR sensor 20 acommand to begin tracking. With tracking enabled (step 146), the IRsensor 20 may be polled to for data (step 147). Preferably, new data isrequested twenty times per second from the IR sensor 20. At step 148,the data generated from polling the IR sensor 20 is checked to ensurethat it is reporting valid data. The data may be considered valid if allof the IR-reflective spheres 38 are visible to the IR sensor 20, thedigitizer pointer 23 is fully inside the IR sensor's 20 working volume,there is no interference between the IR sensor 20 and the digitizerpointer 23, and both the location and rotation information reported arenot null. At step 149, if the data is not deemed valid, then thedigitized point is not used by the system 10 and polling is resumed. Ifthe fifth IR-reflective sphere 38 (i.e. the middle sphere) is visible onthe digitizer pointer 23 (step 150), the process of collectingpositional data for the bend algorithm commences. If the middle sphere38 is not visible, then the data is available to the system 10 only toshow proximity of the IR sensor 20 and IR-reflective tracking array 22(step 151). Points used by the bend algorithm are preferably an averageof several raw elements (step 152). Normally, five points are collectedat this step before the points are processed and made available to thebend algorithm. The position data is averaged using a mean calculation.The directions are averaged in the quaternion representation (raw form)then converted to a unit direction vector. The data is rotated from thespatial tracking system 12 coordinate from into the system 10 coordinateframe using a rotation matrix. At step 153, after all processing, thedata is available for the bend algorithm to collect and process furtheras will be described in greater detail below.

The surgical bending software takes the location and direction data ofthe screw locations as described above and uses one or moregeometry-based algorithms to convert these relative screw locations intoa series of bend instructions. FIG. 11 is a flow chart indicating thesteps of the surgical bending process according to a first embodiment.At the input validation step 154, the system 10 may validate the systeminputs to ensure the rod overhang is greater than zero, validate thesensor setup to ensure that the IR sensor 20 location has been set, andvalidate each of the acquired points. By way of the example, thevalidation of each of the acquired points ensures, for example, thatthere are at least two screw points digitized, no two screw locationsare too far apart, no two screw locations are too close together, andthe span between the superior-most and inferior-most screw locations isnot longer than the longest available rod.

At the transformation step 155, the data may be centered and alignedsuch that the first data point acquired is set at the system 10coordinate's origin and all data is aligned to the x-axis of thesystem's coordinates thereby reducing any potential misalignment of theIR sensor 20 relative to the patient's spine.

At the rod calculations step 156, the system 10 may perform rodcalculations for a straight rod solution, a pre-bent rod solution, and acustom-bend solution. For a straight rod solution, the system 10 firstdetermines the length of a straight rod that will span all of the screwlocations. This length may be calculated to accommodate each of thescrew heads, hex and nose lengths of the rods chosen, and the user'sselected rod overhang length. The system 10 then fits the data to astraight line, if the screw data is within tolerance of the straightline, then the bend instructions will return a straight rod, otherwiseit will return no rod solution and proceed to look for a pre-bent rodsolution. By way of example only, the tolerance may be 2 mm in each ofthe sagittal and coronal planes.

For a pre-bent rod solution, the system 10 first determines the lengthof the shortest pre-bent rod from the available rod from the availablerods (as will be described in greater detail below) that will span allof the screw locations. This length may be calculated to accommodateeach of the screw heads, hex and nose lengths of the rods chosen, andthe user's selected rod overhang length. Next, the system 10 fits thedigitized screw data to a circular arc in 3-dimensional space. If thescrew data is within the tolerance of the arc, then the bendinstructions will return a pre-bent rod solution, otherwise it willreturn no rod solution and proceed to look for a custom-bend rodsolution. By way of example, this tolerance may be 2 mm in each of thesagittal and coronal planes.

FIG. 12 depicts a flow chart of a custom bend algorithm according to oneembodiment. At step 158, screw location and direction data is generatedby the spatial tracking system 12 as set forth above. The data is thenprojected into two planes: the x-y plane (coronal view) and the x-zplane (sagittal view). Each projection is then handled as a 2D data set.At step 159, a fixed size loop is generated over small incrementaloffsets for the first bend location for the end of the rod whichoptimizes the ability of the bend reduction step 162 to make smoothsolutions. At step 160, the system 10 creates a spline node at eachscrew location and makes a piecewise continuous 4^(th) order polynomialcurve (cubic spline) through the screw points. At step 161, the smooth,continuous spline is sampled at a regular interval (e.g., every 1 cm)along the curve to generate an initial set of proposed bend locations.At step 162, as many bends as possible are removed from the initial setof proposed bend locations from step 161 as possible to reduce thenumber of bends the user must execute on a rod in order to fit it into ascrew at each digitized screw point. According to one embodiment, nobend is removed if eliminating it would: (1) cause the path of the bentrod to deviate more than a predefined tolerance limit; (2) cause any ofthe bend angles to exceed the maximum desired bend angle; and (3) causethe rod-to-screw intersection angle to exceed the maximum angulation ofthe screw head. Once the number of bends has been reduced, the 2D datasets are combined and handled as a 3D data set. The 3D line segments arethen evaluated based on distance between each line segment interaction(Location), the angle between two line segments (Bend Angle), and therotation (Rotation) needed to orient the bend into the next bend planeusing the following calculations:Location: ((X ₂ −X ₁)²+(Y ₂ −Y ₁)²+(Z ₂ −Z ₁)²)^(1/2)Bend Angle: arc-cosine(V ₁₂ ·V ₂₃)

-   -   where · is the dot product and V is a vector between 2 points        Rotation: arc-cosine(N ₁₂₃ ·N ₂₃₄)    -   where · is the dot product and N is the normal vector to a plane        containing 3 points.        These calculated numbers are then tabulated to the physical        design of the rod bender 18 and the selected rod material and        diameter. Bend angles account for the mechanical rod bender's 18        tolerance and will account for the rod's material and diameter        based on previous calibration testing performed with mechanical        rod bender 18 and the specific kind of rod. Calibration testing        quantifies the amount of spring-back that is expected when        bending a certain rod material and diameter. By way of        illustration, a 5.5 mm diameter titanium rod's spring-back can        be characterized by a 1^(st) order linear equation:        BA _(A)=0.94*BA _(T)−5.66        where BA_(T) is the theoretical bend angle needed that was        calculated from the 3D line segment and BA_(A) is the actual        bend angle needed to bend the rod to so it can spring back to        the theoretical bend angle. Thus, using this equation, when 20        degrees of bend is calculated from the 3D line segment above,        the “spring-back” equation for that rod will formulate that a        25-degree bend needs to be executed in order for it to        spring-back to 20 degrees. The length of the final rod is the        total of all the calculated distances plus the selected rod        overhang.

Once all of the rod solutions have been generated, the loop is completed(step 163). At step 164, from all of the rod solutions generated in theloop above, the system 10 may output the rod solution having thesmallest maximum bend angle (i.e., the smoothest bent rod). It is to beappreciated that the system 10 may choose the rod solution displayedbased on any number of other criteria. At step 169, the system 10 thengenerates the three-dimensional locations of the bends in space.

Referring back to the flow chart of FIG. 11, from the geometric bendlocations and/or pre-bent rod output of the rod calculations step 156above, the system 10 generates instructions for the user to choose astraight rod, a pre-bent rod, or to custom bend a rod (step 157). All ofthe output instructions are human-readable strings or characters. In allcases, the length of the required rod is calculated as described aboveand is displayed to the user as either a cut rod or standard rod. Forcustom bend solutions, rods are loaded into the bender with the“inserter end” (e.g., one pre-determined end of the rod) into the bendercollet 126. If, due to geometric constraints, the rod cannot be bentfrom the inserter end, then the instructions are flipped, and the cut(or nose) end of the rod is instructed to be put into the bender collet126. The bend instructions are generated from the geometric bendlocations and are given as “Location”, “Rotation”, and “Bend” values aswill be described in greater detail below. These values correspond tomarks on the mechanical bender 18.

FIGS. 13-14 depict a flow chart of a second embodiment of a custom bendalgorithm. In accordance with this second embodiment, the custom bendalgorithm includes a virtual bender used to render a virtual rod. Thefollowing calculations and the flowcharts of FIGS. 13-14 highlight thesteps of this embodiment.

The 3D vector s_(i)=[s_(i) ^(x), s_(i) ^(y), s_(i) ^(z)]T denotes thei′^(th) screw digitized by the user such that the set of N acquiredscrews that defines a rod construct may be denoted ass=[s ₀ , . . . ,s _(N−1)]∈

^(3×N)  (1)It may be assumed that the screws have been collected in order (e.g.superior-most screw to inferior-most screw or inferior-most screw tosuperior-most screw) so the index i can also be thought of as the indexthrough time.

A virtual rod (R) of length L_(r) given in mm is broken down into Nruniformly distributed points, R=[r₀, . . . , r N_(r−1)]. Each rod pointr_(i) is composed of two components, a spatial component and adirectional component r_(i)={r_(i) ^(s), r_(i) ^(d)}, where r_(i) ^(s),r_(i) ^(d)∈

³. The segments between rod points is constant and defined byδ_(i) =|r _(i+1) ^(s) −r _(i) ^(s)|. Let Δ_(d)=Σ_(i=0) ^(a)δ_(i), thenΔ_(N) _(r) ⁻¹ =L _(r).

A virtual bender (B) consists of a mandrel (M) of radius M_(r) (mm).Preferably, though not necessary, the key assumption when bending thevirtual rod around M is the conservation of arc length. For illustrativepurposes only, if a 90° bend is introduced to an example rod R of length100 mm around a mandrel with radius 10 mm to produce a rod {circumflexover (R)}, then∫dR=

  (2)

The virtual rod, R, is bent according to a list of instructions. Eachinstruction consists of a location (I_(l)), rotation (I_(r)), and bendangle (I_(θ)). The location is the position of the rod in the bender andcorresponds to the point directly under the mandrel M. The rotation isgiven in degrees (0°-360°) and corresponds to the amount the rod isrotated from 0 in the collet. The bend angle is given by a single letterthat corresponds to a specific angle in degrees. There is acorresponding notch on the bender with the same letter for the user toselect.

The rod is initialized (step 166) such that the spatial component r_(i)^(s)=[Δ_(i), 0, 0]^(T)|_(i=0) ^(N) ^(r) ⁻¹, and the direction componentr_(i) ^(d)=[0, 1, 0]^(T)|_(i=0) ^(N) ^(r) ⁻¹ which effectively orientsthe virtual rod to be at zero rotation in the virtual bender. For eachbend instruction (step 167), the system 10 rotates the virtual rodaround the x-axis by I_(r) (step 168). The system 10 finds the point{circumflex over (r)}_(i) that matches I_(l). The virtual rod istranslated by −{circumflex over (r)}_(i). Next, each rod point from i toi+M_(r)*I_(θ) is projected onto the mandrel M while preserving segmentlength (step 169-170). The virtual rod is then rotated around the x-axisby angle −I_(r). Next, the system 10 checks that r₀ ^(d)=[0, 1, 0]^(T)to verify that the virtual rod in the collet has the correct directionvector (step 171). At this point, R has approximated the geometry of therod as it would be bent in the physical mechanical bender 18.

The next step is to align the bent virtual rod to the acquired screwpositions (step 172). According to one embodiment, the alignment processhas two stages—first, the system 100 finds the optimum rotation coarsescale (step 174). Second, the system performs the iterative closestpoint iteration algorithm fine scale.

Preferably, the system first initializes the result close to a globalminimum (step 173). In the rod alignment algorithm, this initializationfollows the approach described below:

Using the arc length of the custom rod and the are length of the screws,putative matches from the screws to the rod are produced. This producestwo 3D point sets of equal size. Given two 3D mean centered point setsΣ=[σ₀, . . . , σ_(N−1)] and Γ=[γ₀, . . . , γ_(N−1)], then in the leastsquares sense, it is desirable to minimize

$\begin{matrix}{E = {\frac{1}{N}{\sum\limits_{i = 0}^{N - 1}{\left( {\sigma_{i} - T_{\gamma_{i}}} \right)^{T}\left( {\sigma_{i} - T_{\gamma_{i}}} \right)}}}} & (3)\end{matrix}$Where T denotes the rotation matrix. Let {circumflex over (T)} denotethe optimum 3D rotation matrix, then

$\begin{matrix}{\hat{T} = {\arg\limits_{T}\min\frac{1}{N}{\sum\limits_{i = 0}^{N - 1}{\left( {\sigma_{i} - T_{\gamma_{i}}} \right)^{T}\left( {\sigma_{i} - T_{\gamma_{i}}} \right)}}}} & (4)\end{matrix}$It turns out that {circumflex over (T)}=UV^(T), where

$\begin{matrix}{{C = {{{SVD}(H)} = {U\;{\sum V^{T}}}}}{and}} & (5) \\{H = {\frac{1}{N}{\sum\limits_{i = 0}^{N - 1}{\sigma_{i}^{T}{{\gamma_{i}\left( {{step}\mspace{14mu} 174} \right)}.}}}}} & (6)\end{matrix}$

Due to error potentially introduced by differences in arc length, theproposed solution may not be the global minimum. Thus, the following arerepeated until convergence (step 175):

For each s_(i), find the closest r_(j) (step 176)

Calculate the residual vector e_(i)=s_(i)−r_(j)

Calculate  the  average  residual  vector$\hat{e} = {\frac{1}{N}{\sum\limits_{i = 0}^{N - 1}{e_{i}\mspace{14mu}{\left( {{step}\mspace{14mu} 177} \right).}}}}$

Translate the rod by ê (step 178)

Verify the error is reduced (step 179).

Next the virtual rod is rendered at step 180. The curve may besimplified for rendering purposes by traversing each triad of rod pointsand calculating the angle between the two vectors. If the first triad is{r₀, r₁, r2}, the two vectors are formed as v=r₁−r₀ and w=r₂−r₀. If|v×w|=0, then the middle point of the triad (in this case r₁) isredundant, provides no new information to the geometry of the rod andmay be removed.

It will be appreciated that, in accordance with this embodiment of therod bending algorithm, the virtual bender may be capable of bending arod at any location of any angle perfectly to observe arc length. Usinga virtually bent 3D rod to determine problem screws (i.e. screwlocations with a high screw-rod fit error) may give an accurate fitbetween the actual screws and actual rod before the actual rod is bent.This may be particularly advantageous in certain surgical applicationswhere it is desirable to quantify the amount of offset between a rodsolution and the digitized screw locations as well as input one or moresurgical parameters into the rod bending calculation.

In accordance with the present invention, there is described a thirdembodiment of an algorithm for generating a custom bend which may beutilized in conjunction with the second embodiment. The approach isdirected to one or more algorithms that sample from probabilitydistributions and employ random sampling to obtain a numerical result. AMarkov chain is a sequence of random variables, X₀, X₁ . . . , such thatthe current state, the future and past states are independent.p(X _(n+1) =x|X ₀ =x ₀ ,X ₁ =x ₁ , . . . ,X _(n) =x _(n))=P(X _(n+1)=x|X=x _(n))  (1)Given an ordered set of screws that define a constructS=[s ₀ , . . . ,s _(N−1)]∈

^(3×N)  (2)where s_(i)=[s_(i) ^(x), s_(i) ^(y), s_(i) ^(z)]^(T) denotes the i^(th)3D screw digitized by the user, the system 10 finds the set of bendinstructions that define a rod that fits the screws in an optimum waydefined by an error function. It is to be appreciated that the search ofthe bender space is quite complex as there are several constraints thatmust be observed for the algorithm to produce valid bend instructions(e.g., the bend locations cannot be in close proximity to the screws,the bend locations must be in multiples of 5 mm apart, the bend anglesmust be in multiples of 5°, no bend angle can be greater than 60°,etc.).

In accordance with the second embodiment, the likelihood or errorfunction may be constructed based on how well the virtual rod fits thedata. Here, the rod is fit to the data in the least squares sense. Inthis way, a likelihood function is defined that incorporates, forexample, a prior to prefer fewer bend instructions:

$\begin{matrix}{L = {\prod\limits_{i = 0}^{N_{s} - 1}\;{\frac{1}{\sigma_{s}\sqrt{\pi}}e^{\frac{- {({s_{i} - r_{i}})}^{2}}{\sigma_{s}^{2}}}e^{\frac{- N_{b}}{\alpha}}}}} \\{L = {\left( \frac{1}{\sigma_{s}\sqrt{\pi}} \right)^{N_{s}}e^{\sum\limits_{i = 0}^{N_{s} - 1}\frac{- {({s_{i} - r_{i}})}^{2}}{\sigma_{s}^{2}}}e^{\frac{- N_{b}}{\alpha}}}}\end{matrix}$such that the log-likelihood function may be defined as

$\begin{matrix}{{\log(L)} = {{{- N_{s}}{\log\left( \sigma_{s} \right)}} - {\sum\limits_{i = 0}^{N_{s} - 1}\frac{- \left( {s_{i} - r_{i}} \right)^{2}}{\sigma_{s}^{2}}} - \frac{- N_{b}}{\alpha}}} & (3)\end{matrix}$Where N_(b) denotes the number of bends in the rod, N_(s) denotes thenumber of screw locations, s_(i) is the i′th screw, r_(i) is the i′throd point, and a is the control hyper-parameter for the number of bends(e.g. α=0.05).

As can be seen from equation (3), there has been introduced a prior tocontrol the number of bends introduced into the rod. This probabilisticapproach to bend instruction generation allows for tailoring ofconstraints, for instance, a prior on the severity of the bends couldalso be introduced. Further, a prior could be introduced on how todefine how close to the screws the bends may be located. This prior mayhave a “preferred” value, but probabilistically, there may be an optimalsolution away from this idealized value. By way of example, somehypothesized rules that may be applied to this algorithm include, butare not limited to: birth move: add a bend to the current solution;death move; remove a bend from the current solution; update move:translate rod points along the rod. Use of this embodiment may providemore potential rod solutions to the user.

Details of the system 10 are now discussed in conjunction with a firstembodiment of a method for obtaining a custom-fit rod. The system 10 istypically utilized at the end of a posterior or lateral fixationsurgical procedure after screws, hooks or other instrumentation havebeen placed, but prior to rod insertion. As shown in the flowchart ofFIG. 15, the system 10 obtains position information of the implantedscrew positions and outputs bend instructions for a rod shaped tocustom-fit within those implanted screws. At step 190, pertinentinformation is inputted into the system via a setup screen. At step 192,the user designates the side for which a rod will be created (patient'sleft or right side). At step 194, the system 10 digitizes the screwlocations. At step 196, the system 10 outputs bend instructions. At step198, the user bends the rod according to the bend instructions. Steps190-198 may then be repeated for a rod on the contralateral side of thepatient if desired.

FIG. 16 illustrates, by way of example only, one embodiment of a screendisplay 200 of the control unit 16 capable of receiving input from auser in addition to communicating feedback information to the user. Inthis example (though it is not a necessity), a graphical user interface(GUI) is utilized to enter data directly from the screen display 200. Asdepicted in FIG. 16, the screen display 200 may contain a header bar202, a navigation column 204, device column 206, and a message bar 208.

Header bar 202 may allow the user to view the date and time, altersettings, adjust the system volume, and obtain help information via dateand time display 210, settings menu 212, volume menu 214, and help menu216 respectively. Selecting the settings drop-down menu 212 allows theuser to navigate to system, history, and shutdown buttons (not shown).For example, choosing the system button displays the rod bendingsoftware version and rod bender configuration file; choosing theshutdown option shuts down the rod bending software application as wellas any other software application residing on the control unit 16 (e.g.a neuromonitoring software application); and choosing the history optionallows the user to navigate to historical bend points/instruction datain previous system sessions as will be described in greater detailbelow. Selecting the help menu 216 navigates the user to the system usermanual. As will be described in greater detail below, navigation column204 contains various buttons (e.g., buttons 218, 220, 222, 224, 226) fornavigation through various steps in the rod bending process. Pressingbutton 204 expands/minimizes the details of the navigation column.Devices column 206 contains various buttons indicating the status of oneor more devices associated with the system 10. By way of example,devices column 206 may include buttons 228 and 230 for the digitizer 23and IR sensor 20 components of the system 10, respectively. Pressingbutton 206 expands/minimizes the details of the devices column.Furthermore, pop-up message bar 208 communicates instructions, alerts,and system errors to the user.

FIGS. 16-17 depict an example setup screen. Upon selecting setup button218 on the display screen 200, the system 10 automatically initiates thesetup procedure. The system 10 is configured to detect the connectionstatus of each of its required components. By way of example only, icons228, 230 indicate the connectivity and activity status of the digitizer23 and IR sensor 20, respectively. If one or more required componentsare not connected or are connected improperly, the display 200 may alertthe user to address the issue before proceeding via textual, audio,and/or visual means (e.g., textual messages, audible tones, coloredicons or screens, blinking icons or screens, etc.). According to oneembodiment, the digitizer icon 228 is a status indicator for the activeacquisition and/or recognition of the digitizer and the presence andbackground color of the icon 228 may change to indicate the digitizertracking status. By way of example, the icon 228 may be absent when thesystem 10 is not acquiring screws and does not recognize the digitizer,gray when the system 10 is not acquiring screws and recognizes thedigitizer, green when the system 10 is in screw acquisition mode andrecognizes the digitizer, and red when the system 10 is in screwacquisition mode and does not recognize the digitizer. Pressing button206 expands/minimizes the details of the device column 206. Depending onthe type of surgery, type of patient deformity, etc., it may beadvantageous for the user to choose a digitizer from a selection ofdifferent digitizers. According to one embodiment, pressing icon 228expands a pull-out window for the different stylus options availablewith the system 10 (e.g., styluses 22, 24, 26, 30 as described above).According to another embodiment, the IR sensor graphic icon 230 is astatus indicator for the IR sensor 20. The presence and background colorof the icon 230 may change to indicate the status of the IR sensor 20.By way of example, the icon 230 may be absent when the system 10 doesnot recognize the IR sensor 20, gray when the system 10 recognizes theIR sensor 20 is connected to the system 10, and red when the system 10senses a communication or bump error for the IR sensor 20. Preferably,the IR sensor 20 should be recognized if it is connected afterinitialization of the bending application.

With all of the required components properly connected to the system 10,the user may then input one or more pieces of case-specific informationfrom one or more drop-down menus. By way of example, drop-down menus forrod system 234, rod material/diameter 236, rod overhang 238, proceduretype (not shown), and anatomical spinal levels of the surgicalprocedure) may be accessed from the setup selection panel 232 of thescreen display 200. The rod system drop-down menu 234 allows the user tochoose the rod system he/she plans to use. This selection drives choicesfor the rod material/diameter 236 drop-down menus. By way of example,under the rod system drop-down menu 234, the system 10 may be programmedwith numerous fixation options from one or more manufacturers.Alternatively, it may be programmed with the fixation system selectionsfor one manufacturer only (e.g. NuVasive® Precept®, Armada®, and SpherX®EXT). The user may also choose the combination of rod material (e.g.titanium, cobalt chrome, etc.) and rod diameter (e.g. 6.5 mm diameter,5.5 mm diameter, 3.5 mm diameter, etc.). The drop-down menu 238 formaterial and diameter options may preferably be dependent upon thechoice of rod system. Because the geometry and sizes can vary betweenmanufacturers and/or rod systems, programming the system 10 with thesespecific inputs can aid in outputting even more accurate bendinstructions. The user may also choose the amount of overhang from therod overhang pull-down menu 238. By way of example, the amount ofoverhang may be selectable in 0 mm, 2.5 mm, 5 mm, 7.5 mm, and 10 mmlengths. According to one embodiment, this function prescribes asymmetric overhang on both the superior and inferior ends of the rod.According to another embodiment, this function also prescribes differentoverhang lengths on either end of the rod based on user preference andpatient anatomical considerations. Although not shown, the system 10also contains functionality for accommodating multiple rod diameters andtransitional rods as used, for example in Occipital-Cervical-Thoracic(OCT) fusion procedures

After the setup inputs have been inputted into the setup selection panel232, the system 10 aids the user in setting up the IR sensor 20 in anoptimal position for positional data acquisition. It is to beappreciated that any visual (textual, graphic) indicator may be used toindicate the IR sensor placement instructions. According to someimplementations, an active graphic directs the user to position the IRsensor 20 relative to the digitizer array 22 held static within thepatient's body. As shown in FIG. 17, the user first selects the side ofthe patient the IR sensor 20 is located on by selecting the left sidesensor position button 242 or right side sensor position button 244 inthe IR sensor setup panel 240. Choosing the left or right side sensorposition button 242, 244 activates the IR sensor positioning panel 246such that sensor graphic 248 and a tracking volume box graphic 250appear on the display screen 200. Tracking volume box 252 that moveswith the sensor graphic 248 as the IR sensor 20 is moved. Next, the userpositions the digitizer array 22 into the body of the patient. Oncerecognized by the system 10, a target volume box 252 (which may bedisplayed as white in color) is positioned over the patient graphic 254.Next, the user moves the IR sensor 20 relative to the digitizer array 22until the tracking volume box 250 matches up to the position of thetarget volume box 252. According to some implementations, the sensorgraphic 248 increases in size if it is moved superior to the targettracking volume and decreases in size if it is moved inferior to thetarget volume. According to some other implementations, the trackingvolume box 250 may be color-coded to depict the relative distance to thetarget volume. By way of example, the tracking volume box 250 may bedepicted in red if the distance to the target volume is outside of acertain distance in one or more axes (e.g., outside±8 cm in all 3 axes)and green if within or equal to ±8 cm in all 3 axes. Once the optimalposition of the IR sensor 20 has been ascertained, the setup process iscomplete.

Once the user has completed all of the required steps in the setupscreen, a graphic (e.g., a check) may appear on setup button 218 toindicate such a completion and the system 10 proceeds to step 192 in theflowchart of FIG. 15. Using the GUI, the user designates which side ofthe patient's spine to acquire digitized positional information from byselecting either the Left “L” toggle/status button 220 or Right “R”toggle/status button 222. The user then selects the Acquire Screwsbutton 224 which navigates the display screen 200 to an Acquire Screws(left or right) screen shown by way of example in FIGS. 18-20. InAcquire Screws mode, the display screen 200 includes a sagittal viewpanel 256 and a coronal view panel 258 with spine graphics 260, 262 ineach of the sagittal and coronal views, respectively. Spine graphic 260may flip orientation depending on which side of the spine the user isdigitizing (left or right). Additionally, spine graphic 262 mayhighlight the side of the patient the user is digitizing (left orright). The user may digitize the location of each implanted screwusing, by way of example, the digitizer pointer 23 as described above.As each screw point 264 is digitized, its relative location with respectto the other acquired screw points 264 can be viewed in both sagittaland coronal views via the sagittal view panel 256 and the coronal viewpanel 258 as shown in FIG. 19. Optionally, the last screw pointdigitized may have a different graphic 266 than the previously-acquiredscrew points 264 (by way of example, the last screw point acquired 266may be a halo and the previously-acquired screw points 264 may becircles). The screws locations may be digitized from asuperior-to-inferior or inferior-to-superior direction and according tosome embodiments, the system 10 can detect which direction thedigitization is occurring in after the acquisition of two consecutivescrew point locations. If during the digitization process, the userwishes to delete a digitized screw point, he/she may do so by pressingthe “Clear Point” button 270. If the user wishes to delete all digitizedscrew points, he/she may do so by pressing the “Clear All Points” button268.

Once the digitized screw points 264 are deemed acceptable, the user maypress the “Calculate Rod” button 272 which initiates the curvecalculation preferably using one of the algorithms discussed above. Oncea rod solution has been calculated, a rod graphic 274 populates throughthe screw points 264, 266 and a confirmation graphic (e.g., a check) mayappear on the “Acquire Screws” button 224 to indicate that the system 10has generated a rod solution. Simultaneously, the “Calculate Rod” button272 becomes the “Undo Rod” button 272. If the user presses the “UndoRod” button 272, the rod solution 274 is cleared and the user mayacquire more screw points or clear one or more screw points. After the“Undo Rod” button 272 is pressed, it then changes back to the “CalculateRod” button 272. Optionally, the system 10 may include a visual graphicfor where along a rod the curve calculation is generating a severe bend(acute angle). The user may select “Undo Rod” button 272, perform one ormore surgical maneuvers (e.g. reduce the screw, backup the screw, adjustthe screw head, etc.), redigitize the screw point, and generate a morefeasible solution. If the rod solution is acceptable to the user, theScrew Acquisition step 194 is complete and the system 10 proceeds theBend Instructions step 196 in the flowchart of FIG. 15. Alternatively,although not shown the system 10 may display the offending pointresulting in the severe bend angle in red and offer the next-bestsolution that includes a bend angle falling within a pre-determinedrange of angles for that bender. If the rod solution is acceptable tothe user, the Screw Acquisition step 194 is complete and the system 10proceeds the Bend Instructions step 196 in the flowchart of FIG. 15.

The user then selects the “Bend Instructions” button 226 which navigatesthe display screen 200 to a Bend Instructions (left or right) screenshown by way of example in FIG. 21. The bend instructions within thebend instructions panel 276 allows the user to view the bendinstructions corresponding to the resulting rod solution in the AcquireScrews screen (FIG. 20). By way of example, the bend instructions panel276 contains three fields containing various aspects of the bendinginstruction: upper message field 278, bender instructions field 280, andlower message field 282. By way of example, the upper message field 278may communicate the rod cut length, rod type, and/or rod loadinginstructions to the user (e.g. “Cut Rod: 175.00 mm Load Inserter EndInto Bender”). The bender instructions field 280 displays rows 284 ofbend maneuvers in location 286, rotation 288, and bend angle 290 toperform on the mechanical bender 18 as will be described in greaterdetail below. In the example shown in FIG. 21, there are five rowsindicating five bend instructions. The lower message field 282 maycommunicate the direction of insertion or orientation of implanting therod to the user. For example, the lower message field 282 shown in FIG.21 provides the following sample instruction: “Insert Rod head to foot.”In some implementations, the rod insertion direction into the patient isdependent on the sequence of screw digitization (superior-to-inferior orinferior-to superior). According to one or more preferred embodiments,the bend instruction algorithm takes into account the orientation of theinferior, superior, anterior, and posterior aspects of the rod andensures that these aspects are known to the user. As the instructionsfor use direct the user to load the rod into the bender, the system 10manages which bends are imparted on the rod first based on the severityof the bend angles. The section of the bend instructions with greaterbend angles may be performed first then the straighter bend sections ofthe bend instructions may be performed last. Further, the instructionsmay also direct the user to align a laser line or orientation line onthe rod to an alignment arrow (not shown) on the mechanical rod bender18. This alignment controls the Anterior/Posterior orientation of therod geometry and generates bend instructions accordingly. The userfollows the bend instructions generated by the system 10 for location(location may be color-coded on the bender 18 and on the screen 200 asgreen triangle), rotation (rotation may be color-coded on the bender 18and on the screen 200 as red circle), and bend angle (bend angle may becolor-coded on the bender 18 and on the screen 200 as blue square),sequentially, starting at the first bend instruction and workingsequentially until the final bend is completed. From here, the user mayrepeat steps 190-198 on the rod construct for the contralateral side ofthe patient's spine.

Within a surgical procedure, a user may wish to toggle between left andright screens to view left and right digitized screw points, rodpreviews, and bend instructions for reference or comparison. Selectingthe Left “L” toggle/status button 220 and right “R” toggle/status button222 allows the user to do so. According to one more implementations, theGUI may additionally include a History feature. Selecting the Historybutton (not shown) will allow the user to refer back to any previous rodbending solution. The user navigates to the Bend Instructions screen 226based on choice of the L/R toggle buttons 220, 222 and pressing BendInstruction button 226. If navigating to previous bend instructions, theBend Instructions screen will display previous bend instructions. Oncethe user has selected the desired rod solution, the user then executesthe bends using the mechanical bender 18.

The embodiments described with respect to FIGS. 15 and 18-21 abovecontemplate digitizing the implanted screw positions and outputting bendinstructions for a rod shaped to custom-fit within those implantedscrews. In one or more additional embodiments, the system 10 obtainsposition information of the implanted screws (steps 192 and 194),accepts correction inputs via one or more advanced options features(step 195), and generates for viewing bend instructions for a rod shapedto fit at locations apart from those implanted screw positions (step196) as depicted in the flowchart of FIG. 22. Installing a rod shaped inthis manner could correct a curvature or deformity in the patient'sspine according to a user's prescribed surgical plan. Details of thesystem 10 are discussed now discussed with examples for obtaining a rodbent according to one or more surgical plans.

As depicted in FIG. 23, selecting the “Advanced Options” button 292expands an Advanced Options menu 292 from which the user may perform oneor more corrections to the digitized screw points and the system 10generates bend instructions that will achieve those desired correctionson the patient's spine once the rod is implanted and the screws arebrought to the rod.

In some surgical procedures, a user may wish that the rod bend solutionwill consider a point that is not a digitized screw point in determiningthe bend instructions. According to some implementations, this point isan adjusted distance from the digitized screw point location. Selectingthe “Adjust Points” button 296 from the Advanced Options menu 292navigates the user to an Adjust Points screen as depicted in FIG. 23.Selecting a digitized screw location of interest (for example the screwpoint represented as dot 304 in FIG. 24) highlights the screw point andbrings up an adjust points control 306 in each of the sagittal andcoronal views 256, 258. The user adjusts point 304 to its desiredlocation in the sagittal and coronal planes using arrows 308, 310, 312,and 314. In some implementations, as the point moves, dot 304 changescolor based on the distance from the originally digitized screw locationas shown in FIG. 25. Preferably, that color corresponds to color-codedoffset distance indicator 322 which provides visual feedback to the useras to the distance the point has been adjusted. As depicted by way ofexample, dot 304 appears yellow in FIG. 25 indicating that the point hasmoved 4 mm in each of the sagittal and coronal planes. In someimplementations, the system 10 may have a maximum distance from thedigitized point past which it will not allow the manipulated point toexceed (by way of example only, this distance may be 5 mm). In otherimplementations, this distance may be depicted as a distance (forexample, the numeral 18 in FIG. 48, indicating that a screw point is 18mm from its original location). The user may adjust as many points asdesired in this fashion. The user may reset all adjusted points to theiroriginal configurations via “Reset” button 316 or may undo the lastadjusted point via the “Undo Last” button 318. Once satisfied with theadjusted points, the user may either proceed to one or more additionaladvanced options as set forth below or select “Calculate Rod” 272. Once“Calculate Rod” 272 has been selected, the system 10 generates a rod inwhich the curve traverses the adjusted points, as in FIG. 26, therebycreating a correction-specific rod and providing the user with theability to correct the curvature or deformity in the spine according tohis or her prescribed curve.

According to other implementations, a user may wish for a smoother rodbend. When the “Virtual Point” button 320 (shown by way of example inFIG. 25) is selected, the system 10 allows the user to add an additionalpoint anywhere in between the superior-most and inferior-most digitizedscrew locations. While there is no screw at this location, this point istaken into consideration during the curve calculation and may coerce thecurve into a more natural shape yielding a smoother rod bend. Oncesatisfied with the virtual points, the user may either proceed to one ormore additional advanced options as set forth below or select “CalculateRod” 272 and as described above, the system 10 generates acorrection-specific rod solution 274 that the user may use to correctthe spine to the shape of the rod.

It may be advantageous for some patient anatomies for a user to use apre-bent rod. Use of a pre-bent rod eliminates the need for makingadditional bends to a rod while assuring that a desirable rod curve isachieved. After all screw points have been digitized in the AcquireScrews step 194, selecting the “View Pre-Bent Rod” button 298 from theAdvanced Options menu 292 navigates the user to a “View Pre-Bent Rod”screen as depicted in FIGS. 27-28. Based on the digitized screwlocations shown in FIG. 27, the system 10 calculates and outputs thebest pre-bent rod geometry based on the selected manufacturer's rodsystem that was chosen during the setup step 190 (e.g. NuVasive®Precept®) and displays the best fit virtual pre-bent rod solution 324available on top of the digitized screw points for viewing in thesagittal and coronal views 256, 258 (see FIG. 28). Preferably, thesystem 10 only generates a pre-bent rod solution if the geometry of thepre-bent rod fits the digitized screw points within a predeterminedcurve fitting tolerance (e.g. 7 mm). According to one or moreembodiments (as depicted in FIG. 28), a color-coded offset distanceindicator 322 may provide the user with an indication of the distanceeach screw position will be from the pre-bent rod construct. If the useris satisfied with the pre-bent rod suggestion, the system 10 proceeds tothe Bend Instructions step 196 which displays the corresponding pre-bentrod specifications in the Bend Instructions Screen (FIG. 29). The uppermessage field 278 instructs the user that, based on the digitized screwpoints, an 85.0 mm pre-bent rod is recommended. From here, the user maydecide whether the patient's anatomical and surgical requirements wouldbe better suited with a pre-bent option or a custom-bent option. Armedwith the information from FIGS. 27-29, the user may then adjust thescrew positions to fit the pre-bent rod if needed (e.g., adjust thescrew head, adjust the screw depth, etc.).

In some instances, a user may want to align or correct the patient'sspine in the sagittal plane (i.e., add or subtract lordosis orkyphosis). The system 10 includes a sagittal correction feature in whichthe user is able to measure the amount of lordosis in the spine andadjust angles in the sagittal plane. The system 10 then incorporatesthese inputs into the bend algorithm such that the rod solution includesthe desired alignment or correction.

Selecting the “View Vectors” button 300 from the Advanced Options menu292 initiates the sagittal correction feature. The user may select atleast two points of interest and the system then determines theappropriate vector in the sagittal view. According to the embodimentshown in FIGS. 30-31 and 33, the angles are measured and adjusted basedon the screw trajectory screw axis position) using the digitized screwdata acquired in the Acquire Screws step 194. As shown in FIG. 30, theuser selects at least two screw points of interest (e.g., screw points338 and 342). The system 10 then measures the angle between the screwtrajectories (shown here as 35 degrees). In some implementations, thesystem 10 may measure the total amount of lumbar lordosis by measuringthe lumbar lordosis angle 334 in the superior lumbar spine (shown inFIG. 30 as 15 degrees) and the lumbar lordosis angle 336 in the inferiorlumbar spine (show in FIG. 30 as 35 degrees). Using the angle adjustmentbuttons 328, 330 on the Angle Adjustment Menu 326, the user may increaseor decrease the desired angle correction of the spine in the sagittalplane (i.e., add or subtract lordosis or kyphosis superiorly orinferiorly). As the angle is adjusted, the angular position 336 betweenthe two screw points 338, 342 is changed as well. FIG. 31 illustrates anexample in which the angular position 336 between points 338 and 342 isincreased to 50 degrees). The system 10 may include a color-coded offsetdistance indicator 322 to provide the user with an indication of thedistance each digitized screw position will be adjusted in the sagittalplane as described above. Once the desired amount of angular correctionis achieved, the user may select the “Set” button 332, and then the“Calculate Rod” button 270. The system 10 then displays a rod solution274 incorporating the user's clinical objective for correction of thespine in the sagittal plane as depicted in FIG. 33.

According to the embodiment of the sagittal correction feature shown inFIG. 32, the superior and inferior lumbar lordosis angles 334, 336 aremeasured, displayed, and adjusted referencing anatomy from an importedlateral radiographic image. By way of example, lateral radiographicimage 358 may be inputted into the system 10. The user may touch thescreen 200 and move lines 360 over at least two points of interest (e.g.the superior endplate of V1 and the inferior endplate of V3) and thesystem 10 then then measures the angle between the two lines 360. TheUsing the angle adjustment buttons 328, 330 on the Superior AngleAdjustment Menu 346 or Inferior Angle Adjustment Menu 348, the user mayincrease or decrease the desired angle correction of the spine in thesagittal plane (i.e., add or subtract lordosis or kyphosis superiorly orinferiorly). As either the superior or inferior lumbar lordosis angle isadjusted, the amount of adjustment is dynamically altered in itsrespective angle measurement box (i.e., either superior lumbar lordosisangle box 354 or inferior lumbar lordosis angle box 356). As depicted inFIG. 32, the user adjusts angle lines 360 as part of the inferior lumbarlordosis angle. The system 10 measures this angle as 20 degrees asdepicted in angle measurement field 350. The user then uses button 330in superior angle adjustment menu 346 to increase the angle. This changeis depicted in inferior lumbar lordosis angle box 356. Once the desiredamount of correction is achieved, in this example, it is achieved at 50degrees. The user may then press the capture angle button 352 and thisparameter may be correlated to the digitized screw positionscorresponding to the vertebral levels that those angles were measuredoff of. The system 10 may include a color-coded offset distanceindicator 322 to provide the user with an indication of the distanceeach digitized screw position will be adjusted in the sagittal plane asdescribed above. Once the desired amount of angular correction isachieved, the user may select the “Set” button 332, and then the“Calculate Rod” button 272. The system 10 then displays a rod solution274 incorporating the user's clinical objective for correction of thespine in the sagittal plane as depicted in FIG. 33.

It is to be appreciated that, because patient position (e.g., pelvictilt) may have an effect on the lumbar lordosis measurements, thesagittal correction feature of the system will be able to account forany patient positioning-related deviations. It will also be appreciatedthat in addition to lordotic corrections, the sagittal angle assessmenttool may be useful for other types of surgical maneuvers, including butnot limited to pedicle subtraction osteotomy (PSO) procedures andanterior column reconstruction (ACR) procedures.

In some instances, a user may want to align or correct the patient'sspine in the coronal plane (i.e., correct scoliosis). The system 10includes one or more coronal correction features in which the user isable to view the patient's spine (and deformity) in the coronal planevia anterior-posterior x-rays; measure one or more anatomic referenceangles; and/or persuade one or more screw locations towards a particularcoronal alignment profile by manually or automatically biasing whichdirection the rod bend curve is adjusted. The system 10 may thenincorporate these inputs into the bend algorithm such that the rodsolution includes the desired alignment or correction.

Selecting the “Coronal Correction” button 302 from the Advanced Optionsmenu 292 initiates the coronal correction feature. The user may wish toascertain the degree of coronal deformity by referencing spinal anatomy,measuring the coronal Cobb angles between two anatomical references inthe coronal plane, and adjusting those angles intraoperatively as partof the surgical plan to bring the spine into (or closer to) verticalalignment.

According to the embodiment shown in FIGS. 34-35, the coronal Cobbangles may be ascertained using anterior-posterior radiographic images.Anterior-posterior radiographic image 358 may be inputted into thesystem 10. According to one implementation, the coronal Cobb angle maybe determined by drawing lines parallel with the endplates of the mosttilted vertebrae above and below the apex of the curve and measuring theangle between them. The user may touch the screen 200 and move lines 360over at least two points of interest (e.g. the superior endplate of T11and the inferior endplate of L3) and the system 10 then measures theangle between the two lines 360. Using the angle adjustment buttons 328,330 on the Superior Vertebra Angle adjustment menu 346 and/or theInferior Vertebra Angle adjustment menu 348, the' user may increase ordecrease the desired angle correction of the spine in the coronal plane(i.e., add or subtract correction to make the endplates of the superiorand inferior vertebrae selected more parallel with one another). Aseither the superior or inferior component of the coronal angle isadjusted, the coronal Cobb angle measurement may be dynamically alteredin the coronal Cobb angle measurement box 350. By way of example, inFIG. 34, the starting coronal Cobb angle is 58 degrees. The user usesbuttons 328, 330 to reduce the angle lines 360 between T11 and L3. Oncethe desired amount of correction is achieved (shown, by way of example,in FIG. 35 as a coronal Cobb Angle of 0 degrees), the user may thenpress the capture angle button 352. This parameter may be correlated tothe digitized screw positions corresponding to the vertebral levels thatthose angles were measured off of. The system 10 may include acolor-coded offset distance indicator 322 to provide the user with anindication of the distance each digitized screw position will beadjusted in the coronal plane as described above (not shown here). Oncethe desired amount of angular correction is achieved, the user mayselect the “Set” button 332, and then the “Calculate Rod” button 272.The system 10 then displays a rod solution 274 incorporating the user'sclinical objective for correction of the spine in the coronal plane.

According to the embodiment shown in FIGS. 36-37, the coronal Cobb anglemay be displayed and adjusted referencing anatomy from digitizedlocations of screws placed in the left and right pedicles of thevertebrae of interest. The system links left and right digitized screwlocations for each respective vertebrae (line 361) and measures theangle between the two lines 361 (shown here in FIG. 36 as 58 degrees).According to one implementation, the coronal Cobb angle may bedetermined by selecting the screw location of the most tilted vertebraeabove and below the apex of the curve. Using the angle adjustmentbuttons on the Angle Adjustment menu 326, the user may increase ordecrease the desired angle correction of the spine in the coronal plane(i.e. add or subtract correction to make the endplates of the superiorand inferior vertebrae selected by the user more parallel with oneanother). As the coronal angle is adjusted, the Cobb angle measurementmay be dynamically altered as set forth above. Here, however, instead ofcoronal Cobb angle measurement box 351, the Cobb angle may be displayedalongside the radiographic image (shown in FIG. 36 with a startingcoronal Cobb angle of 58 degrees). The user uses the buttons in menu 326to reduce the angle lines 361 between T11 and L3. Once the desiredamount of correction is achieved (shown, by way of example, in FIG. 37as 0 degrees, the user may then press the “Set” button 332 and thisparameter may be correlated to the digitized screw positionscorresponding to the vertebral levels that those angles were measuredoff of. The system 10 may include a color-coded offset distanceindicator 322 to provide the user with an indication of the distanceeach digitized screw position will be adjusted in the coronal plane asdescribed above (not shown here). Once the desired amount of angularcorrection is achieved, the user may select the “Calculate Rod” button272. The system 10 then displays a rod solution 274 incorporating theuser's clinical objective for correction of the spine in the coronalplane.

According to one or more other implementations of the coronal correctionfeature, the user may select at least two points of interest and thesystem then generates a best fit reference line through all pointsincluding and lying between the at least two points of interest. In someinstances, the ideal correction of the spine in the coronal plane is astraight vertical line extending between the superior-most andinferior-most screw locations of interest. However, depending on apatient's individual anatomy, achieving a straight vertical line may notbe feasible. The user may wish to achieve a certain amount of correctionrelative to the ideal correction. From the display screen, the user mayselect a percentage of relative correction between the screw points asdigitized (0% correction) and the best fit reference line (100%).Furthermore, the system then calculates a rod solution and shows anoff-center indicator 322 to provide a user with an indication of thedistance each screw is from the coronally-adjusted rod construct as setforth above.

According to the embodiment shown in FIGS. 38-41, the user maystraighten all points within the construct (global coronal correction).From the display screen 200, the superior and inferior screw points 362,364 are selected and the system 10 generates a best fit global referenceline 366 through all points 362, 364, 368. Using the Coronal CorrectionMenu 370, the user manipulates the + and − buttons 372, 374 to adjustthe percentage of correction desired. In the example shown in FIG. 36,the amount of desired correction is shown as 100% on the percentagecorrection indicator 376, meaning the rod solution 274 will be astraight line in the coronal plane and all screw locations will beadjusted to fit the rod/line. As depicted in FIG. 40, the system 10 mayinclude a color-coded offset distance indicator 322 to provide the userwith an indication of the distance each digitized screw position will beadjusted in the coronal plane as set forth above. If the user deems thisan acceptable rod solution, the user selects the “Calculate Rod” button272 to view the rod solution 274 (FIG. 41) and receive bend instructionsor proceeds to another advanced feature as will be described in greaterdetail below.

According to the embodiment shown in FIGS. 42-44, the user maystraighten a subset of the screw points within the construct (segmentalcoronal correction). Based on the sequence those points are inputtedinto the system, a best-fit segmental reference line is generatedthrough the points in the direction of the last chosen point. If aninferior point 364 is selected first and then a superior point 362 isselected second, the system 10 will draw the best-fit segmentalreference line 378 superiorly as shown in FIG. 42. Conversely, if asuperior point 362 is selected first and then an inferior point 364 isselected second, the system 10 will draw the best-fit segmentalreference line 378 inferiorly. Using the Coronal Correction Menu 370,the user manipulates the + and − buttons 372, 374 to adjust thepercentage of correction desired. In the example shown in FIG. 43, theamount of desired correction is shown as 100% on the percentagecorrection indicator 376, meaning the rod solution 274 will be astraight line in the coronal plane and all selected screw locations willbe adjusted to fit the rod/line. As shown in FIG. 44, however,unselected screw locations 380 will not be adjusted to fit the rod/lineand their relative locations will be inputted into the system 10 andtaken into consideration when the rod calculation is made. As depictedin FIG. 43, the system 10 may include a color-coded offset distanceindicator 322 to provide the user with an indication of the distanceeach digitized screw position will be adjusted in the coronal plane asset forth above. If the user deems this an acceptable rod solution, theuser selects the “Calculate Rod” button 272 to view the rod solution 274(FIG. 44) and receive bend instructions or proceeds to another advancedfeature as will be described in greater detail below.

According to another embodiment, segmental coronal correction may beachieved relative to the patient's central sacral vertical line (CSVL)instead of a best-fit segmental reference line running through twoselected digitized screw locations. The CSVL is the vertical linepassing through the center of the sacrum that may serves as the verticalreference line for the patient's coronal deformity as well as a guidefor spinal correction in the coronal plane in accordance with thecoronal assessment and correction features of the present disclosure.

FIGS. 45-49 illustrate a method for using the CSVL line for assessingcoronal deformity and achieving coronal correction according to oneembodiment. Preferably, this method commences after all screws areimplanted into the patient and digitized in the manner set forth above.The user generates one or more radiographic images of the sacrum,localizes a superior and inferior point on the sacrum, and marks thosepoints (e.g., implants Caspar pins, marks the patient's skin with amarker, etc.). Next, the user selects the “Alignment” button 506 (FIG.45). Upon such a selection, the user is prompted to digitize the markedskin points representing the superior and inferior sacral landmarks. Asshown by way of example in FIG. 46, box 510 may pop up to instruct theuser of the various steps of the workflow. Here, the superior point onthe sacrum has already been digitized (shown as digitized point 512) andcheck mark 514. Box 510 further instructs the user to “Acquire Point atInferior End.” Selecting “Clear Coronal Alignment Line” 516 tore-digitize the sacral points and/or exit out of the CSVL coronalcorrection feature. Once the superior and inferior sacral points aredigitized, a dashed line 518 representing the patient's true CSVL lineappears on the screen (FIG. 47) and the digitized screw locations 264are reoriented in system 10 relative to the CSVL line 518. The display200 in the coronal view now represents the patient's current coronalcurve relative to a vertical reference (CSVL). From here, the user mayselect two points (i.e., the screw segment) he/she would like to corrector straighten relative to the CSVL. As shown in FIG. 48, by way ofexample, the user selects points 542 and 544. According to oneimplementation, the first point chosen 542 is the point of rotation ofthe segment and the origin of the straightening line 520. The secondpoint 544 determines the direction of the straightening line 520. Thestraightening line 520 may be drawn parallel to the CSVL line 518 as theobjective of coronal correction is to make the spine as vertical aspossible in the coronal plane. If the user deems this an acceptable rodsolution, the user selects the “Calculate Rod” button 272 to view therod solution 274 (FIG. 49) and receive bend instructions. The user nowhas a rod solution he/she can pull the screws to, knowing that it isstraight relative to the CSVL line and therefore providing the desiredcorrection of the coronal deformity. The user will and receive bendinstructions or proceeds to another advanced feature as will bedescribed in greater detail below.

In some spinal procedures (e.g., anterior column deformity correctionprocedures), restoring a patient's spine to a balanced position may be adesired surgical outcome. According to a broad aspect of the invention,the system 10 may include a Global Spinal Balance feature in which thecontrol unit 16 is configured to receive and assess 1) preoperativespinal parameter measurements; 2) target spinal parameter inputs; 3)intraoperative spinal parameter inputs; and 4) postoperative spinalparameter inputs. One or more of these inputs may be tracked and/orcompared against other inputs to assess how the surgical correction isprogressing toward a surgical plan, assess how close the patient's spineis to achieving global spinal balance, and utilized to develop/refine anoperative plan to achieve the desired surgical correction.

Spinal parameters may comprise the patient's Pelvic Incidence (PI),Pelvic Tilt (PT), Sacral Slope (SS), Lumbar Lordosis (LL), SuperiorLumbar Lordosis (↑ LL), Inferior Lumbar Lordosis (↓LL), C7 Plumb Lineoffset (C7PL), and Thoracic Kyphosis (TK), T1 tilt, and SagittalVertical Axis (SVA) measurements. The target spinal parametermeasurements may be a clinical guideline (by way of example only, theSRS-Schwab classification, or a patient-specific goal based on thatpatient's anatomy). Depending on user preference, these spinalparameters may comprise Pelvic Incidence (PI), Pelvic Tilt (PT), SacralSlope (SS), Lumbar Lordosis (LL), Superior Lumbar Lordosis (↑ LL),Inferior Lumbar Lordosis (↓LL), C7 Plumb Line offset (C7PL), andThoracic Kyphosis (TK), T1 tilt, and Sagittal Vertical Axis (SVA)measurements.

FIG. 50 depicts a flowchart indicating the steps of the Global SpinalBalance feature according to one embodiment. At step 390, the system 10inputs a patient's preoperative spinal parameter measurements. Next, thesystem generates theoretical target spinal parameter measurements (step392). One or more target spinal parameter measurements may be optionallyadjusted the user in accordance with a surgical plan a step 394. At step396, a target spinal rod may be scaled to match the patient's anatomyusing the theoretical or adjusted target spinal parameter measurementsfrom step 392 or 394. This scaled target rod may then be displayed 398to the user. Optionally, the system 10 may generate one or moremeasurements (step 400) during the surgical procedure. At step 402, thetarget spinal parameter data may then be adjusted based on theintraoperative measurements from step 400. Finally, the system 10 maygenerate bend instructions for balanced spine correction.

The user may input a patient's preoperative measurements into the system10 as depicted, by way of example in FIG. 52. Selecting the Pre-Opmeasurement button 404 allows the user to input measurements into PI,LL, Superior LL, Inferior LL, C7PL, and TK input fields 408, 410, 412,414, 416, 418, and 420 respectively. Such pre-operative measurements maybe obtained from manual measurement means imported from any number ofcommercially-available desktop and mobile software applications. Thesepre-operative anatomical measurements may be used to understand theimbalance in the patient's deformed spine as well as help determine anoperative plan to implant devices that would adjust or form the spine toa more natural balance (e.g., rods, screws, a hyperlordoticintervertebral implant, etc.).

As depicted in FIG. 52, the global spinal balance feature allows theuser to adjust the patient's anatomical measurement values to the user'spreferred target spinal parameters for a balanced and/or aligned spine.According to one implementation, selecting the target measurement button406 populates measurements into input fields 410, 412, 414, 416, 418,420 that represent an ideal or properly balanced spine. If the useraccepts these target spinal parameters, the system 10 would output atheoretical rod solution comprising rod shapes and curves representingan ideal or properly balanced spine scaled and overlaid onto thedigitized screw points as shown in FIG. 54. The system 10 may alsoinclude a color-coded offset distance indicator 322 to provide the userwith an indication of the distance each digitized screw position is fromthe rod solution in the sagittal and coronal planes as set forth above.Alternatively, if the user seeks to achieve a different alignment, he orshe may use buttons 422, 424, 426 to adjust these target spinalparameters. The user could then refer to the correction indicator 428for an indication of how much correction (relative to the pre-operativeand theoretical spinal parameters) would be achieved based on thoseadjusted input correction values. The user's input correction valueswould then drive the rod bending algorithm (based on the digitized screwlocations) to a rod shape customized to the user's plan for thatparticular placement. The final rod could be positioned within thepatient and the screws and spine would be adjusted to the rod at thedesired alignment.

In accordance with the Global Spinal Balance feature, spinal parameterinputs may be assessed intraoperatively. For example, the user may wishto intraoperatively measure the amount of lumbar lordosis that has beenachieved (for example, after placement of an intervertebral implant). Asdepicted in FIGS. 55-56, the system 10 may include be configured toobtain or import one or more lateral images, generate one or more linesbetween two or more landmarks on the patient's anatomy, determine arelationship between those landmarks, and adjust one or more spinalparameters to be used in generating the rod solution. As shown by way ofexample in FIG. 55, the user first selects the intraoperativemeasurement button 408. Next, lateral radiographic image 358 may beinputted into the system 10. The user may touch the screen 200 and movelines 360 over at least two points of interest (e.g. the superiorendplate of V1 and the superior endplate of V2) and the system 10 thenmeasures the angle between the two lines 360. As shown in FIG. 56, thesystem 10 measures this angle as 15 degrees as indicated in the anglemeasurement field 350. Optionally, the system may compare theintraoperative measurement to the preoperative and/or target spinalparameter value and provide an indication to the user of how muchcorrection has been achieved relative to the pre-operative andtheoretical spinal parameters. Using the angle measurement buttons 328,330, the user may increase the desired angle of correction of the spinein the sagittal plane (i.e., add or subtract lordosis or kyphosis). Asthe angle is adjusted, the amount of adjustment may be dynamicallydisplayed within angle measurement field 350. The system 10 may includea color-coded offset distance indicator (not shown) to provide the userwith an indication of the distance each digitized screw position will beadjusted in the sagittal plane as described above. Once the desiredamount of angular correction is updated, the user may press the “Set”button 332 and then the “Calculate Rod” button (not shown in this view).The system then displays a rod solution 274 incorporating the user'sintraoperative objective for correction of the spine in the sagittalplane.

The user may also wish to intraoperatively measure the patient's pelvicincidence angle. As shown in FIG. 57, selecting the intra-op measurementbutton 408 optionally brings up a PI assessment tool. The system 10obtains a fluoroscopic image 452 of the patient's pelvis. The user firstselects the femoral head button 432 and uses arrows 450 on the PIAdjustment Menu 448 to locate the center point of the femoral head 434.Next, the user selects the posterior sacrum button 436 and uses arrows450 to identify the posterior aspect of the sacral endplate 438. Then,the user selects the anterior sacrum button 440 and uses arrows 450 toidentify the anterior aspect of the sacral end plate 442. With all PIinputs selected, the user may press the “Draw PI” button 446 after whichthe system 10 automatically draws and measures the pelvic incidenceangle 446 for the user.

The illustrative embodiment above included the use of target spinalparameter inputs to determine a target rod shape to restore or improvespinal balance. However, it is to be appreciated that not allembodiments require such a determination. FIG. 51 depicts a flowchartindicating the steps of an intraoperative Global Spinal Balanceassessment feature according to one embodiment. At step 556, the system10 inputs a patient's preoperative spinal parameter measurements. Next,the system generates theoretical target spinal parameter measurements(step 558). One or more target spinal parameter measurements may beoptionally adjusted the user in accordance with a surgical plan at step560. At step 562, the system may measure one or more spinal parametermeasurements intraoperatively and provide one or more indications to theuser how the surgical procedure is progressing. At step 564, the systemmay measure one or more spinal parameter measurements postoperatively toassess the final status of the deformity correction and balanceachieved.

The user may input a patient's preoperative measurements into the system10 as depicted, by way of example in FIG. 52. Selecting the Pre-Opmeasurement button 404 allows the user to input measurements into PI,LL, Superior LL, Inferior LL, C7PL, and TK input fields 408, 410, 412,414, 416, 418, and 420 respectively. Such pre-operative measurements maybe obtained from manual measurement means imported from any number ofcommercially-available desktop and mobile software applications. Thesepre-operative anatomical measurements may be used to understand theimbalance in the patient's deformed spine as well as help determine anoperative plan to implant devices that would adjust or form the spine toa more natural balance (e.g., rods, screws, a hyperlordoticintervertebral implant, etc.).

As depicted in FIG. 53, the global spinal balance feature allows theuser to adjust the patient's anatomical measurement values to the user'spreferred target spinal parameters for a balanced and/or aligned spine.According to one implementation, selecting the target measurement button406 populates measurements into input fields 410, 412, 414, 416, 418,420 that represent an ideal or properly balanced spine. Alternatively,if the user seeks to achieve a different alignment, he or she may usebuttons 422, 424, 426 to adjust these target spinal parameters. Inaccordance with the Global Spinal Balance feature, spinal parameterinputs may be assessed intraoperatively. For example, the user may wishto intraoperatively measure the amount of lumbar lordosis that has beenachieved (for example, after placement of an intervertebral implant). Asdepicted in FIGS. 55-56, the system 10 may include be configured toobtain or import one or more lateral images, generate one or more linesbetween two or more landmarks on the patient's anatomy, determine arelationship between those landmarks, and adjust one or more spinalparameters to be used in generating the rod solution. As shown by way ofexample in FIG. 54, the user first selects the intraoperativemeasurement button 408. Next, lateral radiographic image 358 may beinputted into the system 10. The user may touch the screen 200 and movelines 360 over at least two points of interest (e.g. the superiorendplate of V1 and the superior endplate of V2) and the system 10 thenmeasures the angle between the two lines 360. As shown in FIG. 56, thesystem 10 measures this angle as 15 degrees as indicated in the anglemeasurement field 350. Optionally, the system may compare theintraoperative measurement to the preoperative and/or target spinalparameter value and provide an indication to the user of how muchcorrection has been achieved relative to the pre-operative andtheoretical target spinal parameters. Using the angle measurementbuttons 328, 330, the user may increase the desired angle of correctionof the spine in the sagittal plane (i.e., add or subtract lordosis orkyphosis). As the angle is adjusted, the amount of adjustment may bedynamically displayed within angle measurement field 350.

According to one or more implementations, the user is provided with avisual indication as to how the surgical procedure is proceedingrelative to the targeted plan. By way of example, as once theintraoperative lumbar lordosis measurement is within 10 degrees of theplanned pelvic incidence value, then both buttons will be represented onthe screen 200 as green. Once the intraoperative lumbar lordosismeasurement is greater than 10 but less than 21 degrees of the plannedpelvic incidence value, then both buttons will be represented on thescreen 200 as yellow. Once the intraoperative lumbar lordosismeasurement is equal or greater than 21 degrees, then both buttons willbe represented on the screen 200 as red.

In some circumstances, the user may want to assess the amount/severityof coronal plane deformity and/or intraoperatively ascertain the amountof correction achieved with a given rod bend configuration. The systemmay include a Coronal Offset Assessment feature configured to obtain orimport one or more Anterior-Posterior images, acquire digital positioninformation regarding landmarks on the patient's anatomy, generate oneor more lines between those landmarks, and determine a relationshipbetween those landmarks.

According to some implementations, the system 10 first obtains afluoroscopic image 454 of the iliac sacral region (FIG. 58). The userdigitizes two points 456 and selects the Iliac Line: Set button 460 toestablish a horizontal iliac line 458. Next, the user digitizes themidpoint 462 of the sacrum and selects the CSVL Line: Set button 466 andthe system 10 automatically generates an orthogonal line (CSVL line 464)from the sacral midpoint 462 to the iliac line 458. The system 10 thenobtains a fluoroscopic image 468 of the C7 vertebra as depicted in FIG.59. The user digitizes the midpoint 470 of the C7 vertebra and selectsthe “C7PL: Set” button 474 and the system 10 automatically generates anorthogonal line (C7PL line 476) from the midpoint 470 of C7 to the iliacline 458. Finally, the system 10 calculates the coronal offset distance(in box 476) using the offset distance between the CSVL line 464 and theC7PL line 476 line. As such, the user is given an intraoperativeassessment of the amount of coronal offset corrected or left to becorrected which affords the opportunity to decide if a surgical planninggoal has been achieved or if one or more spinal parameter inputs need tobe updated with respect to coronal alignment.

As set forth above, the system 10 provides the user with thefunctionality to select two points on the spine and generate a best-fitreference line between those two points to which to generate a rodsolution and correct the spine to. In some instances, it may bedesirable to intraoperatively represent the spine's true deformity inthe coronal plane and to correct the spine relative to a pelvicanatomical reference. As such, there is provided a virtual orthogonalreference line through which the user may intraoperatively assess adeformed spine against and/or correct coronal a spinal deformity to.

For purposes of illustration, assume that a user has digitized the screwpoints 264 as shown in FIG. 60 and contemplates performing segmentalcoronal correction (as set forth above) with straightening line 524 asthe best-fit reference line. The user may select the “Virtual T-Square”button 522 to activate the Virtual T-Square feature. FIGS. 61-62describe the Virtual T-Square feature in greater detail. First, the userlocalizes three points of reference on the patient's anatomy via c-armfluoroscopy and marks the location of those anatomical references (e.g.,implants Caspar pins, marks the patient's skin with a marker, etc.). Byway of example, the anatomical points of reference may be the left iliaccrest, right iliac crest, and sacral midpoint. The user may be prompted(via text box, audible alert, and the like) to digitize each of thepreviously-identified anatomical reference points in a manner previouslydescribed herein. As the system 10 registers the digitized location ofthe marks designating the left and right points on the iliac crest,points 528, 530 appear on the screen 200, respectively and a horizontalline 534 representing the iliac line is drawn between the left and rightiliac crest points 528, 530. This is shown, by way of example only as adashed line 534 in FIG. 61. Next, the system 10 registers the digitizedlocation of the sacral midpoint, point 532 appears on screen 200, anddashed line 536 representing the CSVL is drawn superiorly and orthogonalto the iliac line 534. According to one or more preferred embodiments,the system 10 may use one or more algorithms to detect that, when theVirtual T-Square feature is activated, the next three acquired digitizedpoints will correspond to the three anatomical reference points ofinterests. With the CSVL line 536 established the digitized screwlocations 264 may be reoriented in system 10 relative to the CSVL line536, the user may select two points (i.e., the screw segment) he/shewould like to correct or straighten relative to the CSVL as set forthabove. The user may also generate a rod solution, receive bendinstructions, and output a rod to pull the screws to, knowing that it isstraight relative to the CSVL line as explained in detail above.Selecting “Reset” button 316 clears the lines 534, 536 and alladjustments in the Coronal View and returns the adjusted spheres totheir original digitized locations. If the user toggles off the VirtualT-square button 522, the reference lines 526 are cleared and theorientation of the points converts back the best fit 524 within theCoronal View window.

In some instances, in addition to intraoperatively assessing and/orcorrecting the spine's true coronal deformity, it may be furtherdesirable to intraoperatively assess coronal spinal balance. Coronalspinal balance is determined by measuring the offset between the CSVLand a C7. According to some embodiments, the Virtual T-square featuremay be included with a C7 Plumb Line Measurement feature. After the userhas acquired the CSVL line via the Virtual T-square feature 522, the “C7Plumb Line” button 540 is enabled. FIG. 63 describes the C7 Plumb Linefeature in greater detail. First, the user localizes the center of theC7 vertebra via c-arm fluoroscopy and superficially marks the locationof this anatomical reference on the patient's skin (e.g., with an “X”).The user may be prompted (via text box, audible alert, and the like) todigitize each of the C7 vertebra points in a manner previously describedherein. As the system 10 registers the digitized location of the marksdesignating the C7 vertebra, point 558 appears on the screen 200 and avertical line 538 representing the C7 Plumb Line is drawn parallel tothe CSVL and orthogonal to the iliac line 534. This is shown, by way ofexample only as a dashed line 538 in FIG. 63. According to one or morepreferred embodiments, the system 10 may use one or more algorithms todetect that, when the C7 Plumb Line feature is activated, the nextacquired digitized points will correspond to the C7 anatomical landmark.Finally, the system 10 calculates the coronal offset distance using theoffset distance between the CSVL line 536 and the C7PL line 538. By wayof example, a double arrow line is drawn between the two vertical linesto represent the degree of coronal offset, and hence the spinal balanceor imbalance in the coronal plane (shown in FIG. 63 as 10 cm). Accordingto one or more embodiments (not shown), a color-coded coronal offsetdistance indicator may provide the user with an indication of the degreeof coronal offset. By way of example, an offset of 0-2 cm could beindicated with a green double arrow line; an offset of 3-4 cm could beindicated with a yellow double arrow line; and an offset of greater than4 cm could be indicated with a red double arrow line. As such, the useris given an intraoperative assessment of the amount of coronal offsetcorrected or left to be corrected which affords the opportunity todecide if a surgical planning goal has been achieved or if one or morespinal parameter inputs need to be updated with respect to coronalalignment.

From one or many of the features discussed above, once the user hasselected the desired rod solution, the user then executes the bendsusing a mechanical rod bender 18. It is contemplated that the mechanicalrod bender 18 may be any bender that takes into account six degrees offreedom information as it effects bends onto a spinal rod. By way ofexample, according to one implementation, the mechanical rod bender 18may be the bender described in commonly-owned U.S. Pat. No. 7,957,831entitled “System and Device for Designing and Forming a SurgicalImplant” patented Jun. 7, 2011, the disclosure of which is herebyincorporated by reference as if set forth in its entirety herein.According to a second implementation, the mechanical rod bender 18 maybe the bender shown in FIG. 64. First and second levers 106, 110 areshown as is lever handle 108 designed for grabbing the lever 106manually and a base 112 for holding lever 110 in a static position.Second lever 110 has a rod pass through 114 so that an infinitely longrod can be used as well as steady the rod during the bending processwith the rod bending device 18. The user grabs handle 108 and opens itto bend a particular rod by picking an angle on the angle gauge 132 andclosing the handle 108 such that levers 106, 110 are brought closertogether. The mechanical rod bender 18 in other embodiments could beproduced to bend the rod during the handle opening movement as well. Therod moves through mandrel 118 and in between moving die 120 and fixeddie 122. The rod is bent between the two dies 120, 122. Gauges on thebender 18 allow the user to manipulate the rod in order to determinebend position, bend angle, and bend rotation. The rod is held in placeby collet 126. By sliding slide block 128 along base 112, the rod can bemoved proximally and distally within the mechanical rod bender 18.Position may be measured by click stops 130 at regular intervals alongbase 112. Each click stop 130 is a measured distance along the base 112and thus moving a specific number of click stops 130 gives one a preciselocation for the location of a rod bend.

The bend angle is measured by using angle gauge 132. Angle gauge 132 hasratchet teeth 116 spaced at regular intervals. Each ratchet stoprepresents five degrees of bend angle with the particular bend anglegauge 132 as the handle 106 is opened and closed. It is to beappreciated that each ratchet step may represent any suitable degreeincrement (e.g., between 0.25 degrees to 10 degrees). The bend rotationis controlled by collet knob 134. By rotating collet knob 134 eitherclockwise or counterclockwise, the user can set a particular rotationangle. The collet knob 134 is marked with regular interval notches 136but this particular embodiment is continuously tunable and thus hasinfinite settings. Once a user turns knob 134, the user can set the knob134 at a particular marking or in between or the like to determine aparticular angle rotation to a high degree of accuracy. Additionally,base 112 may have a ruler 138 along its length to aid the user inmeasuring a rod intraoperatively.

According to another implementation, the rod bender 18 may be apneumatic or motor-driven device which automatically adjusts thelocation, rotation and bend angle of the rod. By way of example, threemotors may be utilized for each movement. A linear translator motorwould move the rod in and out of the mandrel 118 and moving die 120. Onerotational motor would rotate the rod and moving die 120. The bendcalculations could be converted into an interface program that would runto power and control the motors. The automated bender would lessen thepossibility of user error in following the manual bend instructions. Itwould also increase the resolution or number of bends that can beimparted in the rod making for a smoother looking rod.

While this invention has been described in terms of a best mode forachieving this invention's objectives, it will be appreciated by thoseskilled in the art that variations may be accomplished in view of theseteachings without deviating from the spirit or scope of the presentinvention. For example, the present invention may be implemented usingany combination of computer programming software, firmware, or hardware.As a preparatory step to practicing the invention or constructing anapparatus according to the invention, the computer programming code(whether software or firmware) according to the invention will typicallybe stored in one or more machine readable storage mediums such as fixed(hard) drives, diskettes, optical disks, magnetic tape, semiconductormemories such as ROMs, PROMs, etc., thereby making an article ofmanufacture in accordance with the invention. The article of manufacturecontaining the computer programming code is used either by executing thecode directly from the storage device, by copying the code from thestorage device into another storage device such as a hard disk, RAM,etc. or by transmitting the code for remote execution.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown, by wayof example only, in the drawings and are herein described in detail. Ascan be envisioned by one of skill in the art, many differentcombinations of the above may be used and accordingly the presentinvention is not limited by the specified scope. It should be understoodthat the description herein of specific embodiments is not intended tolimit the invention to the particular forms disclosed. On the contrary,the invention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the invention asdefined herein.

We claim:
 1. A method for intraoperative planning and assessment ofspinal deformity correction during a surgical spinal procedure, themethod comprising: receiving digitized location data of a plurality ofimplanted screws; receiving digitized location data of at least oneanatomical reference point; generating at least one virtual anatomicreference line in a coronal plane based on the digitized location dataof said at least one anatomical reference point; accepting one or morespine correction inputs that straighten one or more digitized screwlocations in the coronal plane relative to the at least one virtualanatomic reference line; and based on the one or more spine correctioninputs, generating at least one rod solution output shaped to engage oneor more of the plurality of implanted screws at locations distinct fromthe digitized location data.
 2. The method of claim 1, wherein thevirtual anatomic reference line is a central sacral vertical line. 3.The method of claim 2, wherein the at least one anatomical referencepoint comprises at least two points that correlate to the central sacralvertical line.
 4. The method of claim 3, wherein the at least two pointsare selected from a position at a left iliac crest, a position at aright iliac crest, and a midpoint of a sacrum.
 5. The method of claim 2,wherein the at least one anatomical reference point comprises two pointsthat lie along the central sacral vertical line.
 6. The method of claim5, wherein the at least one anatomical reference point comprises asuperior point and an inferior point on a sacrum.
 7. The method of claim2, wherein the one or more spine correction inputs comprises aligningall of the digitized screw locations relative to the central sacralvertical line in the coronal plane.
 8. The method of claim 2, whereinthe rod solution output is a vertically straight rod along at least aportion of a length.
 9. The method of claim 1, further comprising:generating at least one measurement value based on at least oneanatomically-based reference point.
 10. The method of claim 1, furthercomprising: generating at least one measurement value based on at leasttwo anatomically-based reference lines.
 11. The method of claim 10,wherein the measurement is an offset distance between said two referencelines.
 12. The method of claim 11, wherein said two reference lines area central sacral vertical line and a C7 plumb line.
 13. The method ofclaim 12, further comprising: assessing an intraoperative spinal balancebased on a relationship between said central sacral vertical line andsaid C7 plumb line and communicate that assessment to a user.
 14. Themethod of claim 13, wherein said relationship is based on a coronaloffset distance between the central sacral vertical line and the C7plumb line.
 15. The method of claim 14, wherein assessing theintraoperative spinal balance includes providing a visual communication,wherein the visual communication is a color in which a first colordesignates an offset distance indicating a balanced spine within acoronal plane and a second color designates an offset distanceindicating an unbalanced spine within the coronal plane.
 16. The methodof claim 9, wherein the measurement value comprises an intraoperativelumbar lordosis angle and a planned pelvic incidence angle.
 17. Themethod of claim 16, further comprising: assessing intraoperative spinalbalance based on a relationship between an intraoperative lumbarlordosis angle measurement and a planned pelvic incidence angle.
 18. Themethod of claim 17, wherein the lumbar lordosis angle and pelvicincidence angle are measured at least once during the surgical spinalprocedure.
 19. The method of claim 18, wherein the relationship is basedon a variance between the intraoperative lumbar lordosis angle and theplanned pelvic incidence angle.
 20. The method of claim 19, whereinassessing the intraoperative spinal balance includes providing a visualcommunication, wherein the visual communication is a color in which afirst color designates a variance indicating a balanced spine within asagittal plane and a second color designates an variance distanceindicating an unbalanced spine within the sagittal plane.